Micro-V, Poly-V & Serpentine Ribbed Belts
Micro-V, Poly-V & Serpentine Ribbed Belts
Micro-V, Poly-V, and serpentine belts are one family of V-ribbed belts: flat belts with small lengthwise V-ribs molded into the underside, sized by section (J, K, L, M), rib count, and effective length. Texas Belting stocks 3,000+ ribbed belts from D&D Global, Megadyne, Bando, Diesel Belting, Gates, and Continental in Houston, TX.
Shop ribbed belts by type
On this page: J/K/L/M sections · Read the numbers · ID with a ruler · Measure a belt · Cross reference · Same belt? · Sheaves · FAQ
What is the difference between J, K, L, and M section belts?
The section letter sets the rib pitch: J ribs sit 2.34 mm apart, K ribs 3.56 mm, L ribs 4.70 mm, and M ribs 9.40 mm. J covers fractional-horsepower equipment, K is the automotive serpentine section, L handles mid-range industrial drives, and M runs high-horsepower machinery. The ribs must match the pulley grooves, so sections never interchange.
| Section | Rib Pitch | Belt Height | Min Pulley Dia | Typical Applications | Shop |
|---|---|---|---|---|---|
| J (metric PJ) | 2.34 mm (0.092 in) | ~3.3 mm | 20 mm (0.79 in) | Small compressors, power tools, floor machines, fitness equipment, appliances | J section belts |
| K (metric PK) | 3.56 mm (0.140 in) | ~4.6 mm | 45 mm (1.77 in) | Automotive serpentine drives (SAE J1459), fans, concrete saws, industrial washers | K / PK belts |
| L (metric PL) | 4.70 mm (0.185 in) | ~7.0 mm | 75 mm (2.95 in) | Compressors above 30 kW (about 40 hp), HVAC blowers, machine tools | L section belts |
| M (metric PM) | 9.40 mm (0.370 in) | ~13.0 mm | 180 mm (7.09 in) | Crushers, paper machinery, large conveyors, agricultural equipment | M section belts |
A smaller PH section (1.60 mm pitch) exists for appliance drives but is rarely encountered in US plants. Published maximum belt speeds drop as the section grows: roughly 60 m/s for J, 50 for K, 40 for L, and 30 for M. Rib pitch, groove dimensions, and minimum diameters follow DIN 7867 and ISO 9982.
What do the numbers on a ribbed belt mean?
Every ribbed belt number encodes three things: effective length, section, and rib count. Industrial imperial numbers put the length first in tenths of an inch: 970K6 is 97.0 in, K section, 6 ribs. Metric numbers put ribs first and length last in millimeters: 6PK2464 is 6 ribs, K section, 2464 mm. Two formulas convert between systems: imperial number divided by 10 = inches, and inches x 25.4 = the metric length number.
| Numbering System | Example | How To Read It |
|---|---|---|
| Industrial imperial | 970K6 | 970 = 97.0 in effective length (divide by 10); K section; 6 ribs |
| Metric ISO (PJ/PK/PL/PM) | 6PK2464 | 6 ribs; K section; 2464 mm effective length |
| Gates automotive | K060970 | K section; 06 = 6 ribs; 0970 = 97.0 in effective length in tenths |
| Dayco automotive | 5060970 | 50-series ribbed belt prefix; 6 ribs; 0970 = 97.0 in effective length in tenths |
Worked conversions:
- 360J6: 360 / 10 = 36.0 in effective length, J section, 6 ribs. Metric: 36.0 x 25.4 = 914 mm, so 360J6 = 6PJ914.
- 970K6: 97.0 in, K section, 6 ribs. Metric: 97.0 x 25.4 = 2464 mm, so 970K6 = 6PK2464 - the same belt Gates lists as K060970 and Dayco as 5060970.
- 6PK1005 in reverse: 1005 / 25.4 = 39.6 in effective length, 6 ribs, K section.
Brands round the metric number differently by a millimeter or two - Dayco catalogs its 97.05 in belt as 6PK2465, not 6PK2464. Match on rib count plus length within a couple of millimeters, not on exact digits.
Identify the section with a ruler: width by rib count
Overall belt width equals rib count times rib pitch, so a ruler and a rib count identify the section. Six ribs across 14 mm is a J belt (6 x 2.34 mm); six across 21.4 mm is a K. Measure across the flat back, count the ribs, divide width by ribs, and match the result to 2.34, 3.56, 4.70, or 9.40 mm.
| Ribs | J Section Width | K Section Width |
|---|---|---|
| 3 | 7.0 mm (0.28 in) | 10.7 mm (0.42 in) |
| 4 | 9.4 mm (0.37 in) | 14.2 mm (0.56 in) |
| 5 | 11.7 mm (0.46 in) | 17.8 mm (0.70 in) |
| 6 | 14.0 mm (0.55 in) | 21.4 mm (0.84 in) |
| 8 | 18.7 mm (0.74 in) | 28.5 mm (1.12 in) |
| 10 | 23.4 mm (0.92 in) | 35.6 mm (1.40 in) |
| 12 | 28.1 mm (1.11 in) | 42.7 mm (1.68 in) |
| 20 | 46.8 mm (1.84 in) | 71.2 mm (2.80 in) |
The same math covers the larger sections: L width = ribs x 4.70 mm, M width = ribs x 9.40 mm.
How do I measure a serpentine belt without a part number?
Wrap a string or narrow flexible tape around the complete belt routing, mark where it overlaps, and measure the string. Hold any spring tensioner near mid-travel while you do it. The string reads outside length; the effective length in the part number is measured at the cord line and runs slightly shorter. Then count ribs and measure width to pin the section.
- Belt still on the machine: run the string around every pulley, following the belt path exactly, backside idlers included.
- Belt in hand: roll it one full revolution along a tape measure, or wrap the string around the outside.
- Belt shredded or missing: walk the string through the empty routing with the tensioner at mid-travel, and count the grooves on a pulley to recover the rib count.
- Ordering: quote the string length as an outside measurement, plus rib count and width. On spring-tensioned drives many techs order the next stock size down from the string number, since the tensioner takes up the slack.
Cross-referencing Gates, Dayco, and industrial belt numbers
Automotive and industrial numbering systems describe the same physical belts, so a cross is a conversion, not a compromise: decode the number to ribs, section, and effective length, then match those three values in another catalog. A Gates K060970, a 970K6, and a 6PK2464 are the same 6-rib, K-section, 97.0 in belt.
| Industrial | Metric ISO | Gates Automotive | Dayco Automotive | Decoded |
|---|---|---|---|---|
| 360J6 | 6PJ914 | – | – | 6 ribs, J section, 36.0 in / 914 mm |
| 645K6 | 6PK1638 | K060645 | 5060645 | 6 ribs, K section, 64.5 in / 1638 mm |
| 970K6 | 6PK2464 | K060970 | 5060970 | 6 ribs, K section, 97.0 in / 2464 mm |
Interchange references are based on manufacturer-published equivalents. Verify dimensions before ordering.
J-section belts carry no automotive-format numbers because accessory drives standardized on the K section. If the number fits none of these patterns it is likely an OEM number - send it over and we will cross it against our industrial and automotive serpentine stock.
Are Micro-V, Poly-V, and serpentine belts the same thing?
Yes - they are marketing and field names for one product, the V-ribbed belt. Micro-V is Gates' trade name, Poly-V is the name most industrial suppliers use, Bando's is Rib Ace, and serpentine describes the snaking route around an automotive accessory drive. The standards behind them are shared: SAE J1459 for automotive K-section belts, ISO 9982 and DIN 7867 for industrial belts and pulleys.
The designations map the same way: a PK belt is a K-section belt and a PJ is a J - metric and imperial numbers describe identical rib geometry, differing only in length units. Whatever name is on the box, match section, rib count, and effective length and the belt will fit.
Poly-V sheaves and groove standards
Ribbed belt pulleys carry 40-degree V-grooves at the section's rib pitch, standardized by DIN 7867 and ISO 9982, so belts and sheaves interchange across brands. We stock J-section Poly-V sheaves in 6, 10, and 16 groove configurations; K, L, and M sheaves are quoted on request.
A belt may run on a sheave with more grooves than the belt has ribs if alignment holds, but never hang ribs off the edge of the sheave. When a ribbed belt keeps failing, inspect the sheave: glazed groove flanks, rounded groove tips, or a belt riding visibly deep mean worn grooves that will eat the new belt too.
Micro-V and Poly-V belt supplier in Houston, TX
Most stocked ribbed belt sizes ship same day from our Houston, TX warehouse, and cross-reference quotes typically come back the same business day. We serve plants, fleets, and OEMs across the Texas Gulf Coast and ship nationwide. Call (888) 203-2358 to confirm availability.
Common ribbed belt selection mistakes
- Matching outside length to the part number. The number encodes effective length at the cord line; a tape around the belt's back reads longer. Treat a string measurement as an outside length and cross to the nearest stock effective length.
- Eyeballing the section from width. A 6-rib J and a 4-rib K are both about 14 mm wide. Divide width by rib count to get the pitch before ordering.
- Ordering by vehicle lookup for an industrial machine. Compressors, mixers, and floor machines often wear automotive-numbered belts; decode the number and buy by dimensions instead.
- Measuring the worn belt and ordering long. Worn ribs sit deeper and measure oversize. Measure the routing or cross the old part number.
- Ignoring minimum pulley diameter. Each section has a floor - 20 mm for J, 45 mm for K, 75 mm for L, 180 mm for M; a heavier section on small pulleys fails early.
- Running the wrong rib count. Fewer ribs than designed cuts capacity roughly in proportion; ribs overhanging the sheave shear off.
When to call
The charts above cover standard J/K/L/M identification. Call for:
- L and M section drive sizing, or wide-sleeve and high-rib-count belts
- Elastic stretch-fit serpentine belts, which measure shorter than the drive by design
- Discontinued OEM numbers that fit none of the decoder patterns
- Belt gone entirely and the routing too tight to string-measure
- Repeat failures that point to sheave wear, misalignment, or tensioner problems
Call (888) 203-2358 or send us what you have.
Frequently asked questions
What do the numbers on a serpentine belt mean?
Ribbed belt numbers encode length, section, and rib count. Industrial style 970K6 reads 97.0 inches effective length, K section, 6 ribs. Metric style 6PK2464 reads 6 ribs, K section, 2464 mm effective length. Automotive numbers pack the same data: Gates K060970 is K section, 06 ribs, 970 tenths of an inch. All three describe the same physical belt.
What does 6PK1005 mean?
6PK1005 is a metric V-ribbed belt designation: 6 ribs, K section (3.56 mm rib pitch, the automotive serpentine profile), and 1005 mm effective length. Divide by 25.4 to convert: 1005 mm is about 39.6 inches. The belt is about 21.4 mm wide - 6 ribs times 3.56 mm.
What is the difference between J, K, L, and M section belts?
The letter sets the rib pitch: J is 2.34 mm, K is 3.56 mm, L is 4.70 mm, and M is 9.40 mm between rib centers. J belts serve fractional-horsepower equipment, K is the automotive serpentine section, L covers mid-size industrial drives, and M handles high-horsepower machinery. Sections are not interchangeable because the ribs must match the pulley grooves exactly.
Are poly-V, micro-V, and serpentine belts the same thing?
Yes. Micro-V is Gates' trade name, Poly-V is the common industry name, and serpentine describes the winding routing on automotive accessory drives. The generic term is V-ribbed belt. Metric and imperial designations also match: a PK section belt is a K section belt and a PJ is a J; only the length units differ.
How do I measure a serpentine belt without a part number?
Wrap a string or flexible tape around the full belt routing, with any spring tensioner held near mid-travel, and mark where it overlaps. That gives outside length; the effective length in the part number runs slightly shorter. Count the ribs and measure overall width to confirm the section, then give all three numbers when ordering. If the belt is missing, walk the string through the empty routing.
How do I convert a PK number to inches?
Divide the PK length by 25.4. A 6PK2464 is 2464 mm, which is 97.0 inches; the industrial equivalent designation is 970K6 - effective length in tenths of an inch, then section, then rib count. Going the other way, multiply inches by 25.4: a 645K6 at 64.5 inches converts to 6PK1638. Brands may round the metric number by a millimeter or two.
How do I tell how many ribs my belt has if it is shredded?
Count the grooves on the pulleys instead. The drive was built for a belt whose ribs match its pulley grooves, so groove count recovers the original rib count even when the belt is torn to pieces. Measure the groove-to-groove spacing on a pulley to confirm the section: 2.34 mm is J, 3.56 mm is K.
Can I use a serpentine belt that is slightly longer or shorter?
Only within the drive's adjustment range. A spring-loaded tensioner absorbs small length differences, but it must stay inside its working travel or the belt slips or runs loose. On fixed-center industrial drives the adjustment slots have to take up the difference. When in doubt, match the published effective length; going one stock size either way is a question for the tensioner, not the belt.
Related products and guides
Need help identifying a ribbed belt?
Send the number on the belt, or a photo with width, rib count, and a string measurement. Our Houston team will decode it and quote the match.
Request a Quote Call (888) 203-2358Last updated: July 2026