Pololu社のユニバーサルアルミ6mmマウントハブ（4-40）

good product and good price

Used on a motor with a 6mm shaft.

Great Mounting hubs.. I thought the 6mm was going to be bigger or same as 1/4" but i had enough to drill them out..

I come back on my previous comment: it is me who follows me deceived dimensions, the tree that I use is not in 6mm but 1/4 ". This hub is fully compatible with Actobotice 6mm shafts. With the right shaft, this hub fits. Room of good quality.

Took me a while to find as I did not know what to call it but that is my problem. I found two problems: 1: it did not come with an allen key as suggested above and 2: when tightened with a lot of torque (my own long allan key) it slipped off the end of the shaft of my motor causing minor damage to my device. In fairness I had a slipring inside the hub which pushed the hub out to the very top of the shaft (still fully through the hub though). To get over the problem I put what I'd claim is excessive pressure on the bolt and I give it a tighten between uses just incase.