This is the cap that holds on the decretive plastics on pinball machines. these have just over a 3mm hole. I designed and used these for my Gottlieb jungle queen pinball, and Williams Aztec pinball, but I'm sure it will work on many others. these are not threaded however since they are plastic they threaded onto the threaded posts of the Aztec just fine and it was just tight enough to hold onto the smooth posts of the jungle queen. in the second photo, I have the new one right beside the original one on the Aztec. in the third photo, I have what it looks like without the cap