I bought a couple of these so I could use more aggressive props on the motors I have with 3mm shafts. I am pretty new to this and started with sow fly props wit hex inserts to fit over the nuts.
I wanted more durable, and more effective props. I needed an adapter.
This adapter will not clamp down onto 3mm threads. You need to cut off the threads and install it in the unthreaded part of the motor shaft. Then it fits fine.
I put a drop of loc-tite on the shaft so the adapter wouldn't come off if I need to change the prop.