This is an EDC knuckle to keep in your pocket as you go about your day. I saw them online but could not justify spending $60+ on it so I just made my own. You definitely won't get multiple punches out of it if you ever go to use it, so make your first punch with it a good one and then run. The hole is about 22 mm. I added the F3D file in case you want to change anything. If you make it please post a make!