I have a cheap Chinese co-axial indicator that works OK, BUT poor design of the part that holds the sweeping probe. It had a very thing wall with an M3 thread to hold the probe. I managed to strip the thread. Made a new part with a thicker wall and an M4 screw with a knurled head so I could feel how tight I was getting it. A lot of setups for a part that my fingers had a hard time with. It is about .250" thick. That's a quarter beside it.