If you've ever assembled a piece of flapack furniture, you've probably encountered a 'cam lock nut'
though you may not have heard/read that term.
The challenge is to model one. 15mm dia. x 12/13mm deep; with the spigot that the cam acts on measuring 6mm dia. x 8mm long with a 4mm shaft.
Warning. This is not trivial. I have not found either an existing model, nor engineering drawings, so its a bit hit and miss..