The Castair 213D is an adjustable belt tensioner motor base for 7.5 HP and 10 HP air compressor motors using the 213T NEMA frame. This base allows quick belt tension adjustment without removing belt guards — a dual bolt design that locks the motor position after adjustment. If you are building or rebuilding a 7.5-10 HP Castair compressor system with a 213T-frame motor, this is the motor mount you need. At $138.91 for the loose base, it is sized and rated for motors in the 7.5-10 HP class.
Product Specifications
- Part Number: 213D
- Motor Frame Compatibility: 213T (7.5 HP motors — specifically the 7-213-3 three-phase motor)
- HP Range: 7.5 HP applications with 213T frame
- Configuration: Loose base (motor not included) — see 213DM for pre-mounted version
- Price: $138.91
213T vs. 215T Frame: Understanding the Difference
This is one of the most common ordering mistakes for 7.5-10 HP compressor motors: Castair lists two different frames in this HP range.
- 213T frame (7-213-3): 7.5 HP three-phase motor — uses the 213D/213DM base
- 215T frame (7-215-1 or 10-215-1/10-215-3): 7.5 HP single-phase and 10 HP motors — uses the 215D/215DM base
The 213T and 215T frames have different mounting bolt patterns and dimensions. They are not interchangeable. Check the NEMA frame designation on your motor nameplate before ordering the base. If you have the 7.5 HP three-phase motor (7-213-3, 213T frame, 130 lbs), you need the 213D. If you have any other 7.5 HP or the 10 HP motor (215T frame), you need the 215D.
How the Adjustable Tensioner Works
The 213D uses a slotted motor mounting design with two lock bolts. To adjust belt tension:
- Loosen the two lock bolts slightly
- Slide the motor along the adjustment slot to increase or decrease belt tension
- Check tension (approximately 1/2" deflection per foot of span under moderate finger pressure)
- Tighten both lock bolts to lock position
No belt guard removal required — this is the practical advantage over fixed-mount bases. On a working shop compressor, belt tension should be checked at every oil change and the ability to do that quickly without partial disassembly makes it more likely to actually happen.
Castair Motor Base Size Chart for Reference
- 184D / 184DM: 5 HP, 184T frame
- 213D / 213DM: 7.5 HP three-phase, 213T frame
- 215D / 215DM: 7.5 HP single-phase and 10 HP, 215T frame
- 254D / 254DM: 15 HP, 254T frame
- 256D: 20 HP, 256T frame
- 284D: 25-30 HP, 284T frame
What's in the Box
- 1x Castair 213D adjustable belt tensioner motor base
- Mounting hardware
Note: Motor not included. For motor-plus-base as a complete assembly, order the 213DM.
When Does a Shop Need This vs. the 213DM
Order the 213D loose base when you have an existing 213T-frame motor that is still serviceable and only the base needs replacement, or when you are sourcing components separately for a new build. Order the 213DM pre-mounted assembly when you need both the motor and the base, or when you want the alignment done at the factory rather than in the field. The price difference between the two reflects the motor cost and factory assembly.
Why Buy From Air Compressor Factory Direct?
We stock Castair motor bases in the complete HP range and can confirm the correct base for your specific motor frame before you order. We have been specializing in industrial air compressor components since 2016. Free shipping, free technical support at 866-217-0063, and full manufacturer warranty on all Castair components.
Call 866-217-0063 for quick answers and help!
