When you need to connect two 3/4" keyed shafts so they turn as one, you have to choose between flexibility and simplicity. A rigid coupling has no moving parts, no flexible element, and no room for misalignment. That's both its strength and its limitation.
Quick verdict
The RC-075-KW is a no-frills one-piece rigid shaft coupling with a 3/4" keyed bore, priced at USD 18.59. If your shafts are already aligned and you want a straightforward, solid connection, this coupling does the job. If you expect vibration, thermal growth, or slight offset, a rigid coupling is the wrong starting point.
Who it suits
This coupling suits fixed-speed or reversing applications where the two shafts are mounted in a way that holds them concentric. The listed specs cover forward/reverse, start/stop, and continuous motion, which covers many motor-to-gearbox or motor-to-leadscrew connections. It's not for applications that need angular or parallel misalignment accommodation.
What stands out
Black-oxide steel finish, one-piece construction, and a 3/16" by 3/32" keyway are the core details. The two hex socket set screws are 5/16-18. Maximum speed is 3,450 rpm and maximum torque is 1,420 in.-lbs. Overall length is 2", outer diameter is 1-1/2", and weight is 11.6 oz. These are concrete numbers you can match against your shaft size and load.
Meaningful trade-offs
Because the coupling is rigid, it cannot tolerate misalignment. The spec sheet explicitly lists "None" for shaft misalignment type, so both shafts need to be true before you tighten the set screws. Torque transfer relies on the key and set screws rather than a clamp or spline, so the keyway must be cut to the stated dimensions. The 3,450 rpm limit is worth noting if your application runs faster.
RC-075-KW 3/4" Rigid Shaft Keyed Coupling
This is a one-piece black-oxide steel coupling with a 3/4" keyed bore, 1-1/2" outside diameter, and 2" overall length. It includes two hex socket set screws. At USD 18.59, it's a direct way to connect 3/4" keyed shafts that are already aligned. The 1,420 in.-lbs torque and 3,450 rpm ratings give you a clear operating envelope. The main limitation is the same as its design: no misalignment allowance, so installation alignment is on you.
Bottom line
If you need a rigid, keyed connection between two 3/4" shafts and can maintain alignment, the RC-075-KW is a well-specified choice. The listed torque and speed ratings give you real boundaries, and the black-oxide finish is appropriate for typical industrial shafts. Just don't expect it to solve shaft alignment problems.
