Found this Brass 36 Mills filler plug on an old Grenade range years ago, thought it would be a good candidate for a sectioned 36m I have. When comparing the threads to the sectioned body something was odd, so I clocked up the thread sizes with a Mazak mills plug and found the brass one has a coarser thread. Normal 36 filler plugs are 9/16 x 20 tpi. This brass one is 9/16 x 16 tpi. What do I have here.
