Its a "clip type thingy" you know one of those clip type thingy..
Dunner know what ya coww it but I call it a clip.
TBH I don't know, its a small box clip, I have a few of them and have purchased them from all over the place in the past. Hobbys used to do them (Or was that hobbies) whichever..
Oh, its Ash by the way. The lid is cut from the top of the box on a band saw then sanded down to get the grain match on the sides.. and no I haven't had any problems with warping (Yet) now you have asked I'm going to get loads..