Timing Pulley Flanges and Bar Stock
Timing Pulley Flanges and Bar Stock
These are the two least self-explanatory line items on a synchronous drive, and between them they answer a lot of the calls that start with "the pulley I need does not exist." A flange is the formed disc that keeps the belt on the teeth. Bar stock is a continuous length of toothed pulley material, uncut and unbored, that a machine shop turns into a pulley of any face width and any bore. Neither one is a part you go looking for by name. You go looking for a pulley you cannot find, or for a belt that will not stay on, and the answer turns out to be one of these.
There are 770 flanges in the flange collection and 988 lengths in the bar stock collection, in Powerhouse, Powerhouse HTD, MX and trapezoidal pitches, available to order and shipped from our Houston warehouse. This page covers the flanging rule as it is actually written, why a synchronous belt tracks off in the first place, what bar stock is for, and exactly what information a shop needs from you to cut a pulley from it.
Shop flanges, bar stock and Powerhouse pulleys
On this page: The flanging rule · Why a belt tracks off · Ordering flanges · What bar stock is · What to specify · Materials · Pitches and profiles · Identify a pulley you have · Reading the part numbers · FAQ
The flanging rule, stated once
The flanging rule gets repeated wrong more often than almost anything else in power transmission, usually as "flange the small pulley" or "flange everything." Here it is as the pulley manufacturers publish it.
Every synchronous drive needs at least one pulley flanged on both sides. That is the floor. On a simple two-pulley drive you satisfy it one of two ways, and only these two ways:
- One pulley flanged on both sides. Normally the smaller one, because it is cheaper to flange, it has less wrap to hold the belt, and it is usually the one that is easier to get at.
- Both pulleys flanged on one side each, on opposite sides. Driver flanged on the motor side, driven flanged on the outboard side, or the reverse. Each flange catches the belt going one way.
Flanging both pulleys on the same side is not one of the options, and it is the mistake people make when they order two identical single-flanged pulleys off a list. The belt is restrained in one direction and completely free in the other.
When both pulleys get flanged on both sides
Three conditions upgrade the drive to four flanges. Any one of them is enough:
| Condition | Why | Flanging |
|---|---|---|
| Center distance greater than about 8 times the diameter of the smaller pulley | A long unsupported span lets the belt develop lateral movement between the pulleys that a single flange cannot arrest | Both pulleys, both sides |
| Vertical shafts | Gravity works on the belt continuously, in one direction, whether the drive is running or not | Both pulleys, both sides. The published minimum is one pulley flanged both sides and the other flanged at least on the bottom, but on a vertical shaft there is no reason to buy the cheaper answer |
| The drive has already thrown a belt | Whatever caused it is still there. Flange it so the next belt stays on the machine while you find the cause | Both pulleys, both sides |
| Serpentine or multi-pulley drives (more than two) | More spans, more chances to walk | Every other pulley flanged both sides, or every pulley flanged on alternating sides around the loop |
Why a synchronous belt tracks off, and what a flange actually does
A synchronous belt runs toward the tighter side. If the two shafts are not parallel, one edge of the belt travels a slightly shorter path than the other, carries more tension, and the belt climbs steadily in that direction until something stops it. The same thing happens if the belt itself is unevenly tensioned, if it was installed with a twist, or if a pulley is sitting cocked on its shaft because a bushing was pulled up unevenly.
There are two distinct misalignments and they do not have the same consequences:
- Angular misalignment is shaft nonparallelism. This is the one that drives lateral tracking. The belt teeth also load unevenly across the face, so the teeth at one edge do the work of the whole belt.
- Parallel misalignment is pure offset, with the shafts still parallel but the pulleys not in the same plane. It does not produce the continuous walk that nonparallelism does, but it is not harmless: the belt is held against a flange for the whole life of the drive, and that is edge wear. On a both-sides-flanged pulley, offset plus a tight flange-to-flange gap is exactly how you chew the edges off a new belt in a week.
Synchronous drives are held to tighter alignment than V-belt drives. Manufacturer white papers put the total allowable misalignment for synchronous belts at about one quarter of a degree, against about half a degree for a classical V-belt drive. A quarter of a degree works out to roughly 1/20 in. of gap over a 12 in. span, so the practical shop check is a tight one: with the drive locked out, lay a straightedge across the machined faces of both pulleys and look for daylight. A gap that varies by more than about 1/16 in. over a 12 in. span is already outside the synchronous limit and has to be corrected rather than flanged around. Measure the angular and the offset components separately and add them, because the belt sees the sum.
Worth ruling out before you blame alignment: a bent or partially collapsed existing flange, a pulley pressed on out of square, a worn bore letting the pulley wobble, a bushing that was greased (never grease a taper), and a drive that was fine until somebody shimmed a motor foot. If the belt is also showing tooth wear or edge cord, work through the timing belt troubleshooting guide before ordering parts.
Flanges are ordered separately, and they are not generic
This is the single most common line item people leave off a purchase order. An unflanged pulley does not ship with flanges. Flanges are separate part numbers, and they are specific to the pitch and to the pulley they go on.
Take a real one. The 80-8M-FS is a steel flange for an 80-groove, 8 mm HTD pulley: 8.386 in outside diameter, 7.545 in inside diameter, formed from 0.09 in material to an overall form thickness of 0.125 in. It is a formed disc, not a flat washer, and the form is what gives it stiffness. It presses onto an unflanged pulley.
Both of those diameters are set by the pulley:
- The inside diameter is machined to the pulley it fits, so the flange locates and grips on that pulley and no other. Change the tooth count and the diameter it has to grip changes with it.
- The outside diameter is sized to stand high enough above that pulley to contain the belt running on it. Change the tooth count and the belt now sits above the flange, which means the flange is no longer a flange.
So a flange for a 72-groove 8 mm pulley does not fit an 80-groove 8 mm pulley, and neither one fits a 72-groove 14 mm pulley. The tooth count in the flange part number describes the pulley, not the flange.
What to put on the purchase order
- Pitch and profile of the pulley. The millimeter number on its own does not identify it. See pitches and profiles below.
- Tooth count of the pulley each flange goes on. Both pulleys, if both are being flanged. Catalog flanges cover 10 to 80 grooves. Anything larger is quoted.
- Quantity per pulley. Two flanges make a both-sides-flanged pulley. A drive upgraded to four flanges needs four flanges, not two.
- Which side or sides, so the drive ends up matching the rule rather than accidentally flanged on the same side twice.
- Material. Steel, aluminum or stainless, matched to the environment rather than to the pulley.
- Face width and belt width, so we can confirm the belt clears between the flanges instead of being pinched.
Flanges are among the least expensive parts on a synchronous drive and among the most expensive to be missing, because a drive waiting on a flange is a drive that is down. If you are ordering pulleys, order the flanges on the same purchase order. Drive components carry a $50 minimum order that can be met by mixing pulleys, bushings, sheaves, sprockets and accessories on one order, so there is no reason to leave them for a second call.
Timing pulley bar stock: what it is and when you need it
Timing pulley bar stock is a continuous length of toothed pulley material, made in one pitch and one tooth count, supplied uncut and unbored, with a plain shank at one end for the chuck. The teeth are already there. A shop parts off a blank at whatever face width the drive needs, bores it, cuts the keyway, machines whatever hub the application calls for, and presses on flanges if the flanging rule calls for them. Nobody has to cut teeth, which is the expensive and error-prone part of making a pulley from scratch.
A real example: 18-5M-PS8A is 18 teeth in 5 mm HTD compatible pitch, aluminum, with 8 in of maximum usable toothed length plus a 1 in shank, weighing 0.69 lb. The specification also says "no sintered or powdered metal," which matters to whoever is machining it: solid material takes a keyway and a set-screw thread predictably, where a sintered blank does not. Listed toothed lengths run from 2 in. to 10 in. in the inch series and 50 mm to 160 mm in the metric series. Longer lengths and tooth counts that are not listed are made to order, so call for lead time on those.
The five situations that send you to bar stock
| Situation | What bar stock gives you |
|---|---|
| A tooth count that does not exist as a catalog pulley | Standard pulley ranges skip counts, especially at the high end. If the ratio you need lands on a count nobody lists, bar stock in that count answers it directly, because bar stock is sold by tooth count |
| A face width that does not exist | Catalog pulleys come in the belt widths the catalog carries. Bar stock is parted to any width, whether that is narrower than the smallest listed pulley or wide enough to carry two or three belts side by side |
| A special hub | Bolt circles, flywheel faces, extended hubs, hubs on the opposite side, a shoulder to locate against a bearing, an integral coupling face, a bushed bore in a series the catalog part does not offer |
| An obsolete pulley with no equivalent | The machine is thirty years old, the pulley is unmarked, and no current part matches the bore, hub length and face together. A blank cut from bar stock reproduces the mounting exactly |
| Prototype and short-run development | Ratio changes during commissioning without waiting on custom tooling, and without committing to a production quantity |
What we need from you to machine a pulley
Six items are mandatory and three more save a round trip. Send them together and the quote comes back on the first pass.
| What | Detail that matters |
|---|---|
| 1. Pitch and profile | A bare "5 mm" will not do it. A 5 mm Powerhouse, a 5 mm HTD and a 5 mm MX pulley all put tooth centers 5 mm apart and are not the same tooth form. If you have the belt, give us the belt part number and we will work back from it |
| 2. Tooth count | Sets the pitch diameter: PD = tooth count x pitch / 3.1416. Count the grooves on the old pulley or work back from the ratio you need |
| 3. Face width | The toothed face is normally a little wider than the belt. If the pulley is flanged, the flange-to-flange gap has to clear the belt with room for offset, not sit hard against it |
| 4. Bore and keyway | Finished bore size and tolerance, keyway width and depth, and whether you want a set screw over the key. If you want a bushed bore instead, name the bushing system, because the bore is machined for that series specifically and the bushing is a separate line item |
| 5. Hub style | Hub on one side, hub on both sides, hubless, hub in or hub out relative to the face, plus the overall length through bore. This is what makes an obsolete pulley reproducible |
| 6. Material | See the table below. Drives the cost, the inertia and the service life more than anything else on this list |
| 7. Flanging | Which sides, from the flanging rule above, and in what material |
| 8. Operating speed | Give us the rpm. High-speed drives can call for dynamic balancing, and that has to be specified before the part is made, not after it vibrates |
| 9. Quantity and a drawing | A dimensioned sketch, a photograph of the old part next to a rule, or the old part itself. Any of the three beats a description |
Materials, and what each one is for
Bar stock is listed in aluminum and steel only. Flanges are listed in steel, aluminum and stainless. Finished pulleys are made in a wider range, and the choice there is a real engineering decision rather than a preference. If you need a blank or a flange in a material outside those lists, it is a made-to-order part, so call for lead time.
| Material | Where it earns its place | What to watch |
|---|---|---|
| Steel | Highest torque capacity and the best tooth-face wear resistance. Takes a keyway and a set screw without deforming, and takes a welded hub. The default for high-torque 8 mm and 14 mm drives and for anything with shock loading | Heavy, so higher rotating inertia on an accelerating drive. Will rust unless plated or black oxide finished |
| Cast iron | Large diameters at sensible cost, with good vibration damping. Machines cleanly. Common on the big driven pulley of a reduction | Brittle under impact. Heavy. Not a choice for a drive that gets struck or dropped |
| Aluminum | Roughly a third the density of steel, so low inertia. The right call for servo, indexing and high-acceleration drives, and for any pulley a person has to lift onto a shaft alone. Corrosion resistant bare, and anodizes well | Softer tooth faces wear faster under high load or abrasive dust. A bare aluminum bore can fret or gall on a steel shaft, so consider hard anodizing or a steel-bushed bore on a heavily loaded fit |
| Acetal (POM) | Light, quiet, self-lubricating and non-marking. Resists most plant chemicals and washdown, and unlike nylon it is dimensionally stable in water, which is why it shows up on wet lines. Common on light packaging and food-adjacent conveyors | Low load capacity. Continuous service temperature is commonly published around 180 deg F; confirm the figure for the grade supplied. Not a torque part |
| Polycarbonate | Transparent, so belt engagement and debris can be seen through the guard while the machine runs. Impact resistant and light. Used in instrument, laboratory and light inspection equipment | Attacked by a long list of solvents and some alkaline cleaners, and prone to stress cracking around a bore. Softer tooth faces than acetal under sustained load |
| Stainless | Washdown, food and beverage, pharmaceutical, marine and chemical exposure where a plated steel pulley will not survive the cleaning regime. Also the material of choice where rust particles cannot be tolerated in the product | Costs more and machines slower, and the 300 series work-hardens. Name the grade you need rather than saying "stainless" |
Pitches and profiles
Pitch is the distance from the center of one tooth to the center of the next. Profile is the shape of that tooth. They are separate facts, and mixing them up is what causes belts to skip on pulleys that look correct.
| Family | Pitches | Notes |
|---|---|---|
| Powerhouse | 2, 3, 5, 8 and 14 mm | The manufacturer's own profile line, coded 2P through 14P. Miniature drives and servo positioning at the small pitches, general industrial at 8P and 14P. Flange and bar stock listings in this profile cover the 2, 3 and 5 mm pitches. 1,310 pulleys in the collection |
| Powerhouse HTD | 3, 5, 8 and 14 mm | The curvilinear metric profile with the largest installed base in industry. Product data describes these as HTD compatible in each pitch, coded 3M through 14M. 745 pulleys in the collection |
| Powerhouse MX | 5, 8 and 14 mm | A manufacturer line designation coded 5MX, 8MX and 14MX, positioned for high-torque, low-speed drives. Treat it as its own profile family. 642 pulleys in the collection |
| Trapezoidal (inch) | XL 0.200 in, L 0.375 in, H 0.500 in | Straight-flank teeth. The older American series, still everywhere on legacy machinery and light drives |
The flange and bar stock listings also carry pitch codes that sit outside those four families, including MXL (coded MP), LT and the metric T2.5, T5 and T10 series, plus AT5 and AT10 in bar stock. Search the collection for your pitch code, or call with the pitch you need and we will tell you what is listed and what has to be made.
How to identify a timing pulley you already have
Work in this order. Each step narrows the field, and doing them out of order wastes the measurement. Everything below is done with the machine stopped, locked out and verified at zero energy, and with the guard back on before it runs again.
Step 1: pitch, measured across ten teeth
Lay a steel rule along the belt, not the pulley, and measure from the center of one tooth to the center of the eleventh. That is ten pitches. Divide by ten. Measuring a single tooth-to-tooth interval multiplies your reading error by ten when you extrapolate. Measuring ten and dividing divides that error by ten instead.
| Profile | One pitch | Ten pitches |
|---|---|---|
| 2 mm | 2.00 mm | 20.0 mm |
| 3 mm | 3.00 mm | 30.0 mm |
| 5 mm | 5.00 mm | 50.0 mm |
| XL | 0.200 in (5.08 mm) | 2.000 in (50.80 mm) |
| 8 mm | 8.00 mm | 80.0 mm |
| L | 0.375 in (9.525 mm) | 3.750 in (95.25 mm) |
| H | 0.500 in (12.70 mm) | 5.000 in (127.0 mm) |
| 14 mm | 14.00 mm | 140.0 mm |
The pair that catches people is XL against 5 mm. One tooth apart they are 5.08 mm and 5.00 mm, a difference of eight hundredths of a millimeter that no rule in a toolbox will resolve. Across ten teeth they are 50.80 mm and 50.00 mm, and 0.8 mm is a difference a steel rule shows you plainly. The same arithmetic separates MXL (2.032 mm, so 20.32 mm over ten) from a 2 mm pitch (20.0 mm) at the small end.
Step 2: profile, trapezoidal or curvilinear
With the belt off and the drive locked out, look into a groove in good light, or press a piece of modelling clay into it and look at the section you pull out.
- Trapezoidal teeth have straight flanks and a flat top: a clear trapezoid in section, with a distinct land between teeth. XL, L and H are trapezoidal.
- Curvilinear teeth are rounded, a shallow arc running root to root with no flat land at the tip. HTD, MX and Powerhouse are curvilinear.
That distinction is easy. The hard one is that curvilinear profiles resemble each other closely, and a rounded 8 mm tooth does not tell you whether the pulley is HTD or MX. Settle that from the part number, from the machine drawing, or by calling us with photographs. Do not settle it by eye.
Step 3: face width
Measure the toothed face across the pulley, and separately measure the belt width. If the pulley is flanged, measure the clear gap between the flanges. The face is normally wider than the belt. If the belt is as wide as the face, or wider, that is a finding in itself.
Step 4: flanging, and what it tells you
Record which sides of each pulley are flanged before you take anything apart. Then check it against the flanging rule. If the drive turns out to be flanged on the same side twice, or unflanged on a long center distance, you have found something worth fixing on the way back together. That is a better result than the part number you came for.
Step 5: bore, keyway and hub
Measure the bore, the keyway width, and the length through the bore, and note whether the bore is plain, bushed for a taper-lock or QD bushing, or split taper. Bushings are sold separately from the pulley, so if the replacement is a bushed part, the bushing is its own line item. A replacement that matches pitch, profile, tooth count and width and then does not fit the shaft has not saved anyone a shutdown. There is more on pulley and sprocket selection on our timing pulleys and sprockets page, and the standard catalog sizes are on the stock timing belt pulleys page.
Reading the part numbers
Both families encode everything you need, once you know where the fields sit.
Bar stock: tooth count, pitch, PS, length, material
| Part number | Reads as |
|---|---|
| 20XL-PS8S | 20 teeth, XL pitch, Pulley Stock, 8 in of toothed length, Steel |
| 18-5M-PS8A | 18 teeth, 5 mm HTD compatible pitch, Pulley Stock, 8 in of usable toothed length, Aluminum |
| 40T5-PS160A | 40 teeth, T5 pitch, Pulley Stock, 160 mm of toothed length, Aluminum |
- PS means Pulley Stock: a full bar of toothed material, not a finished pulley.
- The pitch code carries the profile as well as the number. 5M is 5 mm HTD compatible, 5P is 5 mm Powerhouse, 5MX is 5 mm MX, MP is MXL, and XL, L and H are the inch trapezoidal series. The letters matter as much as the digits.
- The length field is the toothed area, in inches or millimeters depending on the series. It does not include the shank.
- The shank is a plain, un-toothed length at one end, 0.75 in to 1 in on the parts we list, for the chuck to grip. It is not usable pulley material, so do not count it in your yield, and read the shank length off the specification table for the exact part number.
- Material letters: A is aluminum and S is steel, and those are the only two materials the bar stock listings carry.
- Working out yield: divide the toothed length by your finished face width plus the width of one parting cut, and leave material for facing each blank.
Flanges: pulley tooth count, pitch, F, material
| Part number | Reads as |
|---|---|
| 80-8M-FS | Flange for an 80-groove 8 mm HTD pulley, Steel |
| 80-8M-FA | The same flange in Aluminum |
| 64-14M-FSS | Flange for a 64-groove 14 mm HTD pulley, Stainless Steel |
The leading number is the tooth count of the pulley the flange fits, not a feature of the flange itself. That is why "one 8 mm flange" is not an order we can fill, and why the tooth count has to come across with the request. The listings run from 10 to 80 grooves, so a flange for anything larger is a quoted part.
Frequently asked questions
Do timing pulley flanges come with the pulley?
Only if the pulley itself is a flanged part. On the pulley listings, a flanged part carries a Flange Diameter and a Flange Material in its specification table, and an unflanged part does not, so read the table before you order. Flanges bought on their own are separate part numbers, listed for pulleys from 10 up to 80 grooves. There is no catalog flange above 80 grooves, so if a large driven pulley has to carry them, call and we will quote it.
On a two-pulley drive, which pulley should be flanged?
Either one pulley flanged on both sides, normally the smaller one, or both pulleys flanged on one side each with the flanges on opposite sides. Those are the only two correct arrangements. Flanging both pulleys on the same side leaves the belt unrestrained in one direction and is the common ordering mistake.
When do both pulleys need flanges on both sides?
Three conditions, any one of which is enough: the center distance is more than about eight times the diameter of the smaller pulley, the drive runs on vertical shafts, or the drive has already thrown a belt. On serpentine drives with more than two pulleys, flange every other pulley on both sides or flange every pulley on alternating sides around the loop.
My belt keeps coming off. Will a flange fix it?
A flange will keep the belt on the machine. It will not straighten the drive. A synchronous belt tracks toward the tighter side, which almost always means the shafts are not parallel, a pulley is sitting cocked on its shaft, or the base is not level. A belt held against a flange by that tracking force wears its edge away and eventually fails at the tensile cord. Fit the flanges the rule calls for, then lock the drive out, find the misalignment and fix it.
How do I know which flange to order?
A flange is specific to the pitch and to the pulley diameter. The part number carries the pulley tooth count, the pitch and the material, as in 80-8M-FS for a steel flange on an 80-groove 8 mm HTD pulley. Give us the pitch, the tooth count of each pulley, how many sides you are flanging, the material, and the belt width so we can confirm it clears between the flanges.
What is timing pulley bar stock?
A continuous length of toothed pulley material in one pitch and one tooth count, supplied uncut and unbored with a plain shank at one end for the chuck. A shop parts off a blank at any face width, bores it, cuts a keyway, machines the hub it needs and presses on flanges. The teeth already exist, so nobody has to cut a tooth form. Listed toothed lengths run from 2 in. to 10 in. in the inch series and 50 mm to 160 mm in the metric series.
What do you need from me to have a pulley machined from bar stock?
Six things: pitch and profile, tooth count, face width, bore and keyway, hub style and material. Adding the flanging requirement, the operating rpm and a dimensioned sketch or a photo of the old part next to a rule usually gets the quote back on the first pass. If you have the belt, send its part number and we will work the pitch and profile back from it.
How do I tell an XL pulley from a 5 mm pulley?
Measure across ten teeth on the belt and divide by ten. XL is 0.200 in, which is 5.08 mm, so ten pitches measure 50.80 mm. A 5 mm pitch measures 50.00 mm over ten. That 0.8 mm difference is easy to read on a steel rule, where the 0.08 mm difference over a single tooth is not. The profiles also differ: XL teeth are trapezoidal with straight flanks, and 5 mm metric teeth are curvilinear and rounded.
Is Powerhouse MX the same profile as HTD?
Treat them as separate profile families. MX is a manufacturer line designation coded 5MX, 8MX and 14MX, positioned for high-torque, low-speed drives. Sharing a nominal pitch with HTD does not establish that the tooth forms interchange, and we do not publish an interchange rule between them. Call (888) 203-2358 with the belt and pulley part numbers before mixing profiles on a drive.
Can I add flanges to a pulley that is already on the shaft?
Lock the drive out and pull the pulley first. These flanges press on with interference, and pressing one onto a pulley still mounted risks bending the flange and driving the pulley along its shaft. The belt has to come off for the job regardless, so take the pulley with it, press the flange on properly, and reset the alignment when it goes back.
Which material should the pulley be?
Steel for torque, shock and wear. Cast iron for large diameters at sensible cost. Aluminum where inertia matters, on servo and high-acceleration drives, or where somebody has to lift it. Acetal for light, quiet, wet or non-marking duty. Polycarbonate where you want to see through it. Stainless for washdown, food, pharmaceutical and chemical exposure. Bar stock itself is listed in aluminum and steel only, so a blank in any other material is a made-to-order part; call for lead time.
Related products and guides
Need a flange, a blank, or a pulley that does not exist?
Send the pitch, tooth count, face width and bore, or a photo of the old part next to a rule. We will confirm the profile, the flanging the drive should have, and what it takes to cut it. Everything ships from our Houston warehouse; call for lead time.
Request a Quote Call (888) 203-2358Last updated: August 2026