In my lab we have dressing tools for sharpening grinding wheels. The tools are diamonds mounted on a steel shank and the shank fits into a custom holder with a set screw in our machine (pictured).
The hole in the tool holder is rather large so that it can fit a variety of tool shank diameters. We have a tool with a shank diameter much smaller than the hole diameter, so it has this metal ring wrapped around it to increase its diameter so that it fits tightly in the holder hole. The ring has a gap on one side so that it can be tightened on the shaft.
My question is: What do you call this piece of metal used to increase the diameter of a small shaft? My first thought was to call it a "split collar" or a "split ring" but that doesn't yield anything similar on a Google search.
The reason I am wondering is that we have other dressing tools that are too small to fit in this holder and I would like to buy more of these metal pieces so that we don't need to keep re-using the one we have. But I can't find it if I don't know what it's called.