This is an XLR cable clip for a microphone boom pole. It's used to secure the cable to the boom pole so that it doesn't dangle around and make noise when recording.
There are three different files. They start smaller and get larger to accommodate the diameter of the boom pole. The one that I have has a three section telescoping rod system, which is why three different diameters are needed.
The cable end of the clip fits a standard 6mm wide XLR cable. The width of the part of the clip will vary based on which boom pole you're using and the size of it, but these are the three that worked for me.