Summary This is a small brick that can connect to Lego-style bricks. It is useful for putting on keys and sticking the keys to a mounted Lego baseboard as a key holder. The key ring DOES fit in between the nubs on a flat Lego. I printed mine in wood PLA and it turned out great, except for the fact that support got suck inside of it. I would recommend printing it with the nubs down to avoid this issue.