The Castair P3B615SD is a 3-groove (3B) replacement motor pulley with an SD-style taper-lock hub and 6.15" outer diameter. Three grooves mean this pulley runs three matched B-section belts, significantly increasing power transmission capacity compared to 2-groove designs — appropriate for higher-HP compressor motors where two belts are not sufficient to handle the torque without slipping. The SD hub uses a taper-lock bushing (sold separately) so the same pulley can be adapted to different motor shaft diameters.
Note: Cast Air did not provide a dedicated manufacturer product page for this pulley. Specifications are drawn from the product listing and standard 3B SD-hub pulley engineering conventions. Call us before ordering to confirm the correct SD bushing size for your motor shaft.
Why Three Grooves?
A 3B motor pulley is used when the motor power and torque exceed what two B-section belts can reliably transmit. On compressors in the 3-5 HP range — and on some heavy two-stage compressors — running three belts distributes the drive load, reduces per-belt tension, and eliminates belt slip during the loaded part of the compression cycle. The tradeoff is higher belt replacement cost, but in exchange you get better belt life (lower tension per belt), smoother power delivery, and a drive system that handles the motor's output without overdrivng individual belts.
Pulley Specification Details
- Groove Profile: 3B (three B-section V-belt grooves)
- Hub Type: SD taper-lock (bushing required, sold separately)
- Outer Diameter (OD): 6.15"
- Application: Motor-side pulley for higher-HP belt-drive air compressors
- Compatibility: Cast Air belt-drive compressors using SD-hub motor pulleys and B-section belts
- Part Number: P3B615SD
SD Hub — How It Works
The SD taper-lock system uses a standard SD bushing that slides into the pulley's tapered bore. The bushing is available in multiple shaft sizes, allowing the same pulley to mount on motors with different shaft diameters. Once installed, the taper draws the bushing tight against the pulley bore as the mounting screws are torqued, creating a concentric, vibration-resistant fit. When the motor needs to be replaced, back out the mounting screws, the taper releases, and the bushing can be transferred to the new motor or a new bushing can be ordered for a different shaft size.
SD vs. SK Taper-Lock Hubs
- SD hub: Larger flange diameter than SK. Used on larger OD pulleys and higher-torque applications. The SD bushing is a specific size — confirm your pulley is SD-series before ordering a bushing.
- SK hub: Smaller standard. Used on smaller to mid-size pulleys in the Cast Air lineup. Not interchangeable with SD.
- The P3B615SD uses SD bushings — order accordingly. If you are not sure which bushing your application uses, call us with the pulley part number and motor shaft diameter and we will identify the correct bushing.
When Does a Shop Need the P3B615SD?
- Original 3-groove SD-hub motor pulley is worn, cracked, or damaged
- Rebuilding a higher-HP Cast Air compressor that factory-shipped with a 3B SD-hub motor pulley
- Motor replacement on a 3-belt drive system where the pulley can be reused with a new bushing
- Upgrading from a 2-groove system because belts are slipping under load — requires matching 3-groove flywheel on the pump side
Technical Specifications
- Part Number: P3B615SD
- Manufacturer: Cast Air (Castair)
- Groove Type: 3B (three B-section V-belt grooves)
- Hub Type: SD taper-lock (bushing sold separately)
- Outer Diameter: 6.15"
- Belt Section: B-section (three matched belts)
- Price: $105.88
- Manufacturer Data: Product page not available — specifications from product listing data
What Is Included
- 1x Castair P3B615SD motor pulley (SD hub)
SD bushing and three B-section matched belts are not included. Specify your motor shaft diameter when ordering to get the correct SD bushing. Belts must be ordered based on your drive center distance.
Why Buy From Air Compressor Factory Direct?
Getting a 3-belt SD-hub drive system right requires matching components — correct bushing bore, correct belt section and length, correct flywheel groove count on the pump. We have been working with Cast Air compressor systems since 2016 and can help you source everything needed in one order. Free shipping, free tech support, full warranty.
- Cast Air specialist since 2016
- Free shipping on all orders
- Free tech support — we help identify the correct SD bushing and belt set for your application
- Full manufacturer warranty on all Cast Air parts
- System-level sourcing — pulley, bushing, and belts together
Call 866-217-0063 for quick answers and help!
