I picked up a recovered 25Lb projectile and in cleaning it up noticed that the threads for the fuse were damaged. I cleaned them up as best I could but the fuse that I have (No. 119 Mark I drill) wouldn’t screw in.
Unfortunately I couldn’t find a 2" 14tpi thread chaser anywhere, so I machined one. You’ll note there is no rake on the teeth like you would see on a tap. The reason is that I wanted to clean the existing threads, not cut new ones. If you chase a thread with a tap, you run the risk of removing the existing thread, ending up with (essentially) an oversized bore.
I’m pleased to say that it worked perfectly and the fuse now screws in easily. Note that I took these pictures after completing the process, which is why the chaser threads are covered with crap!