I was on the lathe today for my Rotring 600 (making a practice cap) and had some brass… I made a new bolt, threaded it for standard 4-40 threads (instead of the miniscule 2-56 threads of the original Acetal bolt) and put a new screw and bushing in. The tiny bushing was the hardest thing to make, but I ended up getting one. I made it a bit more streamlined, the bottom of the bolt head is about .010″ off the body of the pen. This pen is definitely a keeper. The bolt is mirror polished and actuates the pen very smoothly.