M4 knurled thumb nut

thingiverse

For me, I needed replacement knurled adjustment knob for a second-hand telescope. The scope (an Orion SkyQuest XT6) uses M4 threads, and when I bought it, it came with nothing. This is a very simplistic design, but it could be expanded upon, or even enlarged for different bolt sizes. It's a little recessed on each side to allow for panhead bolts and nuts being out of the way and more flush with the knob itself.