RC-037 Black Oxide Plated Mild Steel Rigid Coupling, 3/8" Bore, 3/4" Outside Diameter, 1" Length, 1/4"-20 x 3/16" Set Screw

Fits

Works great. The price was reasonable and the build quality was exceptional. Would buy again when needed.

These will work perfectly to connect a steel shaft to a 3/8" motor armature.

For a while I thought that the set screws used a odd size hex key that I didn’t have. After going through all my metric and SAE hex keys (I have about 100 hex keys of various sizes), the closest fit was a 1/8” hex key. I tried 5 different 1/8” hex keys to tighten the set screws, and all of them were a tad too small for the set screw hex holes. You can tighten the set screws to a decent amount, but if you want to really crank them down, the hex key will undoubtedly slip and strip the set screw or the hex key. I measured the bore of the coupling with my Starrett calipers, and it read 0.3745” (within 5 mills of 3/8”), so other than the set screw issue, it fits just fine on my stepper motor’s 3/8” shaft.

Clamps down very good. Nice fit and function.Arrived faster than expected. Would buy from them again.

I have a 3/8" round D shaft on the motor connected to a 3/8" threaded rod. This coupler holds tight on both the motor shaft and the threaded rod.

Worked perfectly. Needed to swap out the engine on my old ariens snowblower, and the new engine interfered with the shaft used to move the throw chute. Used it to add an extension into the shaft before the universal joint and works perfectly.

The set screws do not bite into the rod well and pulls off. I replaced with bolts and it works.