[David Kirkham]

Oh yes! Back to the bolts!

The bolts are 7/16 BSF--or British Standard Fine. If you look closely, you can see the bolts actually have a shoulder on them that fits down into the upright. The threads on the bolt are 55 degrees instead of the standard 60 degree threads that are universal today. I remember looking at the bolt under the optical comparator with Professor Kohkonen. We were perplexed by the 55 degree threads--until his face lit up and he said, "I bet those are Whitworth threads!" He was right. He convinced the Sandvik salesman to "donate" some 55 degree threading inserts to the university which Professor Kohkonen eventually gave to me for all the work I helped him with in the labs. I still have those inserts in the top drawer of my tool box! I remember making my first bolts out of 4130 chromoly. Chromoly was the buzz word then (and now). You wouldn't believe how many people think chromoly is made in heaven. It has SERIOUS drawbacks. I will get into that a little later. As I look back it wasn't the best choice for a number of reasons. Today I would make them from 17-4 PH H1150.