My I Hollis carries the optional Provisional proof mark showing it was given this proof in the finished state along with the definitive so appears to have been made after 1868.
I am a Craftsman, spent over .35 years in the machinist trade. I tapped a lot of holes in that time. It is near impossible to change the pitch of the thread without it showing up. In changing from 26 to 28 TPI you will change the width of each thread by about ..003". This accumulates so after about 5 threads the original thread will be cut in about half. All threads appeared full down to the bottom of the nipple seat.
