[rotorwrench]

Since the inside clearance on the crab cap is based on diameter or radius from the center, a person could machine themselves a go/no-go tool that would just be a gauge to slide down inside the cap for crab types and see if it goes in straight into the recess where the cap fit the distributor housing with a minimum radius to fit between the electrodes on one end then the other end would be maximum radius. If minimum goes in smoothly and maximum doesn't then a person would know if it is in spec or not. If both go then it is either worn out or too much clearance from the get go. If neither go in, a person could use prussian blue or something to see if they can mark the electrodes. A person could make something up on a lathe with a bit of work. I wouldn't be surprised if the manufactureres didn't use such a tool to check them every so often. If they don't now, then they should start to. It's a pain to get new parts that are not made worth a crap and it seems the ignition parts are the worst these days.