4Pcs 3.17mm to 3.17mm Rigid Motor Shaft Coupling Coupler Sleeve Coupling Adapter for 3D Printers RC Motor Accessories

They work well to connect a 8mm motor to a 12mm axle.

Worked great for exactly what I needed them for. I ended up Machining these down to a different size and I was able to machine it cleanly though I'm sure that's not what most of you are buying it for

I used these for a custom rock tumbler I made and they work perfectly.

Good selection

I am happy with this item. I ordered these for a CNC project I'm working on and they worked out great. The machining was well done and the included screws worked great with a little blue thread locker. The shafts run true with minimal run out at full speed. This type of coupler requires your shafts to be very well aligned. If you are worried about it a lovejoy or spring type coupler might be a better choice as they can handle a slight amount of misalignment. This wasn't a problem in my application and they are working great! I'd definitely recommend these couplers.

These couplers fit perfectly!. The grub screw holes are nice and clean, no burs from drilling or tapping. the grub screws themselves fit hassle free, and everything seems really well centered. Nice job!!

Inside diameters are .06mm to large, this puts the center of the shaft .03mm off. When attached to the motor there was .18mm of run out at the end of the 22mm coupler. Useless for any precision applications.