We supply LOTS of these to school orchestra customers whose cellos and basses have the non-removable, tubular endpins (not saying we recommend these endpins, but we are happy to get them working, if you have one). Chromed, rectangular head wing screw fits Ulsa (large-diameter aluminum tubular endpin) and some other European bass endpin sockets. Save having to replace your entire endpin assembly over a lost or broken screw! We are still researching other brands with which this may be compatible, so for now, we can just say it works with Ulsa endpins. If your endpin screw is broken off, and you can't remove the remaining piece, see our repair department for having it extracted. If it's broken and you don't know what screw will fit in it, you can even mail in your entire endpin socket and we will mail it back to you with a new screw (at additional cost).