I have been asked many times to release this so I finally decided to. It's a GoPro knob replacement for the original long one.
You will need to provide the bolt.
So just print this as you would anything else. You will need your own bolt, I get mine from Mcmaster Carr. This is there description:
Metric 18-8 Stainless Steel Hex Head Cap Screw, M5 Size, 45MM Length, .8 mm Pitch, Fully Threaded
And their part number is 91287A331
If you want the matching acorn nut it's part# 94000A037
While the bolt should fit snuggly, I highly recommend using JB Weld to epoxy them in place. Even the originals from Gopro benefit from this.