I feel a little stupid having to resort to a forum for this! (But hey, I'm in my first year of work.)
I have designed a barrel assembly for a paintball gun. It consists of two tubes that screw together. Not terribly complicated at all. However, when fully tightened there are details on the two parts that need to line up. What is this called?! I know the threads have to be (blank.) I've racked my brain and Googled my brains out with no results. :confused: