A while ago, I was working on 6 different kitless pens at the same time.
I figured I'd save some time in retooling by doing all of the drilling, tenon cutting, tapping and threading for them all at once. Makes sense right? Drill 6 cap blanks, thread them, move on.
Sounds good, BUT (BIG BUT), Some were 13mm triple start and others were 14mm triple start. Well, I got the streams crossed (Ghost Busters reference), and ended up turning and threading a 13mm tenon on the barrel of a pen that I had made the cap 14mm. OOPS!!
I was more than a little upset as the material was some rather pricy 5 swirl yellow & black Nikko Ebonite.
I put the cap blank back in the collet chuck, drilled the threads out and epoxied in a piece of black ebonite turned down to fit. After letting the epoxy fully cure, I re-drilled it for 13mm threads and tapped it. I was lucky, if you aren't looking for it, you cannot see the recovery.
Our mistakes truly are how we learn!!