Bored-to-Size (BTS) V-Belt Sheaves
Mounting: Fixed bore with set screw and keyway (no bushing required)
Belt Sections: Classical A and B, plus FHP 3L, 4L, 5L
Grooves: 1 to 4
Series: AK, AKH, BK, BKH, 2AK, 2BK, and combination series
Material: Cast iron
Brands: Gates, Continental/ContiTech
In Stock: Same-day shipping from Houston
Bored-to-size (BTS) sheaves are fixed-bore V-belt pulleys that mount directly to the shaft with a set screw and keyway. Unlike QD sheaves, BTS sheaves do not require a separate bushing. The bore is machined to the final shaft diameter at the factory, so the sheave ships ready to install on the specified shaft size.
BTS sheaves are designed for light to medium duty applications where cost is a priority and the sheave is unlikely to need frequent replacement or shaft size changes. They are the standard choice for small fans, blowers, light pumps, appliances, and OEM equipment running on A section or B section V-belts. For industrial applications above 1 HP or drives that require periodic maintenance, QD sheaves are generally the better choice.
BTS Sheave Series
BTS sheaves are organized by series, with each series designating the belt section and groove count. The series letter tells you the belt section, and the number prefix (if present) tells you the groove count.
| Series | Details |
|---|---|
| AK | 1 groove, A section. The most basic BTS sheave. Light duty fans, blowers, and small pumps. ODs from 2.5" to 6"+. |
| AKH | 1 groove, A section, heavy web. Stronger hub construction than standard AK for slightly higher loads. Same groove profile. |
| 2AK | 2 grooves, A section. For drives using two A-section belts. Common on dual-belt fan and blower setups. |
| BK | 1 groove, B section. Medium duty single-belt drives. Larger ODs and higher power than AK series. |
| BKH | 1 groove, B section, heavy web. Stronger hub for higher loads. Same groove profile as BK. |
| 2BK | 2 grooves, B section. For drives using two B-section belts. Pumps, fans, and light conveyors. |
| AK/BK Combo | 1 groove A + 1 groove B. Allows running either an A or B belt on the same sheave. Useful for OEM flexibility. |
| 3L / 4L / 5L | FHP (fractional horsepower) sections. Very light duty. Small appliances, residential fans, and low-power OEM equipment. Fixed bore. |
BTS Part Number Decoder
BTS sheave part numbers encode the series, outside diameter, and bore size. Once you understand the format, you can identify the sheave specs at a glance.
| Example | What It Means |
|---|---|
| AK30 x 5/8 | 1 groove, A section, 3.0" OD, 5/8" bore. |
| AKH41 x 3/4 | 1 groove, A section heavy web, 4.1" OD, 3/4" bore. |
| 2AK30 x 5/8 | 2 grooves, A section, 3.0" OD, 5/8" bore. |
| BK50 x 7/8 | 1 groove, B section, 5.0" OD, 7/8" bore. |
| 2BK60 x 1 | 2 grooves, B section, 6.0" OD, 1" bore. |
| AK25 x 1/2 | 1 groove, A section, 2.5" OD, 1/2" bore. Smallest common BTS sheave. |
The bore size is a permanent dimension on BTS sheaves. Unlike QD sheaves, you cannot change the bore after purchase. Make sure to specify the exact shaft diameter when ordering. Contact us if you need help confirming the right bore.
Available Bore Sizes
BTS sheaves are stocked in standard bore sizes with keyway. Common bores include:
| Bore Range | Notes |
|---|---|
| 1/2" | Smallest standard BTS bore. Small fans, appliances. |
| 5/8" | Very common. Light fans, blowers, small pump motors. |
| 3/4" | Most popular BTS bore. Matches many fractional HP motor shafts. |
| 7/8" | Common on 1/2 to 1 HP motors. |
| 1" | 1 HP motors. Upper end of typical BTS range. |
| 1-1/8" to 1-1/2" | Available on larger BK and 2BK sheaves. Less common. Approaching QD territory. |
BTS vs. QD: When to Use Each
| Factor | Details |
|---|---|
| Use BTS When | Application is under 1 HP. Cost is the primary concern. Sheave will rarely be removed. Shaft size is known and fixed. 1 to 4 grooves is sufficient. A or B section belt. |
| Use QD When | Application is above 1 HP. Maintenance access matters. Multiple shaft sizes are possible. More than 4 grooves are needed. Any belt section (A through E, 3V, 5V, 8V). |
For a detailed comparison with sizing examples, see our Sheave Selection Guide.
Common Applications
| Application | Typical BTS Sheave |
|---|---|
| Small exhaust fans | AK series, 1 groove. 3" to 5" OD. 1/2" to 3/4" bore. |
| Furnace blowers | AK or BK series, 1 groove. 3.5" to 6" OD. 5/8" to 7/8" bore. |
| Small centrifugal pumps | BK or 2BK series. 4" to 6" OD. 3/4" to 1" bore. |
| Bench grinders/saws | AK series, 1 groove. 2.5" to 4" OD. 1/2" to 5/8" bore. |
| OEM equipment | AK, BK, or combo series. Varies by machine. Fixed bore matches OEM motor shaft. |
| Residential/commercial HVAC | AK or 2AK series. 3" to 5" OD. 1/2" to 3/4" bore. Light duty air handlers. |
Installation Notes
Step 1: Confirm the bore matches your shaft diameter exactly. BTS sheaves have no adjustment for bore size.
Step 2: Slide the sheave onto the shaft and align the keyway with the shaft key.
Step 3: Position the sheave at the correct location on the shaft for belt alignment with the mating sheave.
Step 4: Tighten the set screw against the key (not directly against the shaft surface). Tighten to the manufacturer's recommended torque.
Step 5: Check belt alignment and tension. Both sheaves should be parallel and aligned within 1/16" per foot of center distance.
Brands We Carry
| Brand | Products |
|---|---|
| Gates | Light Duty BTS sheaves in AK, AKH, BK, BKH, 2AK, 2BK, and combination series. Full bore range. |
| Continental | BTS sheaves for A and B sections. Competitive replacement option for HVAC and light industrial. |
We cross-reference BTS sheave part numbers between Gates, Continental, Browning, Martin, and other manufacturers. Send us any part number and we will confirm the match.
Related Pages
Frequently Asked Questions
What does bored-to-size mean?
Bored-to-size (BTS) means the sheave bore is machined to the final shaft diameter at the factory. The sheave ships ready to install on the specified shaft with a set screw and keyway. No separate bushing is needed. This is different from QD sheaves, which use a removable bushing and can fit multiple shaft sizes.
Do BTS sheaves need a bushing?
No. BTS sheaves mount directly to the shaft with a set screw and keyway. The bore is already machined to size. This makes BTS sheaves simpler and less expensive than QD sheaves, but the bore cannot be changed after purchase.
What belt sections do BTS sheaves come in?
BTS sheaves are primarily available for A section and B section classical V-belts, plus FHP sections (3L, 4L, 5L). They are not available for C, D, E, or narrow wedge (3V, 5V, 8V) sections. For those sections, QD sheaves are the standard.
What is the difference between AK and BK sheaves?
AK sheaves have A-section grooves (1/2" top width) for A-section V-belts. BK sheaves have B-section grooves (21/32" top width) for B-section V-belts. The letter indicates the groove profile, and the "K" indicates the BTS (bored-to-size) product line. A "2" prefix (2AK, 2BK) indicates two grooves.
What is an AKH or BKH sheave?
The "H" stands for heavy web. AKH and BKH sheaves have the same groove profile as standard AK and BK sheaves, but with a thicker, stronger hub construction. This allows them to handle slightly higher loads and provides more material around the bore for better set screw retention. They are used when the application is near the upper limit of BTS duty capacity.
Can I re-bore a BTS sheave to a larger size?
This is not recommended. BTS sheaves are cast iron with a hub designed for the factory-specified bore. Drilling or reaming to a larger bore removes material from the hub and can weaken it, leading to cracks or failure under load. If you need a different bore, order the correct size or switch to a QD sheave with a removable bushing.
When should I use a BTS sheave instead of a QD sheave?
BTS sheaves are the right choice when cost is the priority, the application is under 1 HP, the shaft size is known and fixed, the sheave will not need frequent removal, and 1 to 4 grooves is sufficient. For drives above 1 HP, drives needing frequent maintenance, or applications requiring more than 4 grooves, QD sheaves are the better option. See our Sheave Selection Guide for a detailed comparison.
Can Texas Belting cross-reference BTS sheave part numbers?
Yes. We cross-reference between Gates, Continental, Browning, Martin, and other manufacturers. Send us the part number from your existing sheave and we will confirm the equivalent. Submit a part number or call 888-203-2358.
