This is a 2x1 Gridfinity rivet/snap/etc. setter holder. It's intended for a six-piece Craftool Pro rivet-setting set from Tandy but the dimensions of the tools and contents of the kits seem to be pretty standard so it'll probably work for other products as well.

It consists of five circular holes to hold the setting tools and a rectangular slot to hold to the anvil.

This is a pretty tall bin because the tools tend to be heavy and I don't want them falling out.