The Castair P2B975SK is a 2-groove (2B) motor pulley with an SK-style taper-lock hub and 9.75" outer diameter. The SK designation means this pulley uses a standard SK bushing (sold separately) rather than a fixed bore — which lets you adapt it to a range of motor shaft diameters by selecting the correct SK bushing for your shaft size. This is the largest 2-groove motor pulley in the Cast Air SK-hub lineup and is used on higher-HP belt-drive compressors where maximum drive ratio from the motor side is required.
Note: Cast Air did not provide a dedicated manufacturer product page for this pulley. Specifications are drawn from the product listing and standard SK-hub 2B pulley engineering conventions. Contact us before ordering to confirm bushing compatibility and fitment for your specific compressor.
Understanding SK Taper-Lock Hubs
An SK hub is a taper-lock bushing system. The pulley itself has a tapered bore that mates with a matching SK bushing. The bushing is bored to your specific shaft diameter (common sizes: 1-1/8", 1-3/8", 1-5/8", etc.) and has a keyway and set screws. You install the bushing on the shaft, slide the pulley onto the bushing, and the taper draws tight as you torque the mounting screws — creating a secure, concentric fit. SK-hub pulleys can be reused with different motors by swapping bushings, making them the practical choice for industrial installations where motors get replaced periodically.
Pulley Specification Details
- Groove Profile: 2B (two B-section V-belt grooves)
- Hub Type: SK taper-lock (bushing required, sold separately)
- Outer Diameter (OD): 9.75"
- Application: Motor-side pulley for belt-drive air compressors
- Compatibility: Cast Air belt-drive compressors using SK-hub motor pulleys and B-section belts
- Part Number: P2B975SK
What the 9.75" OD Means for Pump Speed
This is the largest 2B motor pulley in the Cast Air SK lineup. A 9.75" motor pulley paired with a 14" pump flywheel produces a drive ratio of approximately 1.44:1 — meaning a 1,750 RPM motor drives the pump at about 1,214 RPM. For most single-stage pumps this is above the normal operating range, so this pulley is typically found on two-stage or heavy-duty Cast Air pump designs that are rated for higher RPM, or paired with a motor and flywheel combination specifically engineered for this drive ratio. Do not use this as an upgrade on a compressor not designed for it.
When to Choose SK Hub vs. Fixed Bore
- SK hub (this pulley): Requires a separate SK bushing sized to your motor shaft. Allows the same pulley to work with different shaft diameters by swapping the bushing. Best for commercial/industrial applications where motor replacement is anticipated.
- Fixed bore: Machined to one specific shaft diameter. Simpler installation, lower cost, correct for direct replacement when motor shaft is unchanged.
- If your original motor pulley was SK-hub, replace with SK-hub and the matching bushing. Do not substitute a fixed-bore pulley — the hub geometry is incompatible.
When Does a Shop Need the P2B975SK?
- Original 9.75" SK-hub motor pulley is worn, cracked, or damaged
- Rebuilding a heavy-duty Cast Air compressor that factory-shipped with the P2B975SK
- Motor replacement on a compressor where the SK bushing can be reused on the new motor shaft
- Installing a different shaft-size motor where a new SK bushing is needed but the pulley OD remains the same
Technical Specifications
- Part Number: P2B975SK
- Manufacturer: Cast Air (Castair)
- Groove Type: 2B (two B-section V-belt grooves)
- Hub Type: SK taper-lock (bushing sold separately)
- Outer Diameter: 9.75"
- Belt Section: B-section (two matched belts)
- Price: Contact for current pricing
- Manufacturer Data: Product page not available — specifications from product listing data
What Is Included
- 1x Castair P2B975SK motor pulley (SK hub)
SK bushing and B-section matched belts are not included. Specify your motor shaft diameter when ordering to get the correct SK bushing for your application.
Why Buy From Air Compressor Factory Direct?
SK-hub pulley systems require matching components — the right bushing for your shaft size, the right belt length for your drive center distance. We have been selling Cast Air parts since 2016 and can help you identify all the components you need in one order. Free shipping, free tech support, and full manufacturer warranty on every Cast Air part.
- Cast Air specialist since 2016
- Free shipping on all orders
- Free tech support — we help you select the correct SK bushing and belt
- Full manufacturer warranty
- Complete system sourcing — pulley, bushing, and belts all from one order
Call 866-217-0063 for quick answers and help!
