Bafang recommended set of 1/2 inch drive M33 sockets specifically designed to tighten the lockrings of the mid drive BBS02 and BBSHD motors. There are two sockets, one designed for the inner lockring with 4 notches, and a second desinged for the outer lockring with sixteen notches. The shape of the motor makes it a little difficult to get a super snug fit with typical spanner wrenches, but with help from these sockets you will be able to tighten the lockrings properly by using a torque wrench and tighten to spec (50-60 N.m). Your mid drive motor will never come loose again with these tools. Sold individually or as a pair (save 10$ when bought as a pair). Do the job right the first time with the right tools.