Posted by David Sherman on Tuesday, June 10, 2003 at 5:42PM :
In Reply to: Re: Buy the set? posted by Ken See on Tuesday, June 10, 2003 at 5:23PM :
"British Whitworth" was the first standard thread series in wide use. Many of the New England tool and machine makers in the mid-1800s adopted it in the US before the UNC and UNF (SAE) series' were standardized. Aside from the 1880s-vintage planer, the only other things I've found with Whitworth threads are an old hand-forged auger brace and a screw in a jack plane, both of which my great-grandfather used in his cabinet shop in the 1880s.
I've been told that some English cars and bikes used Whitworth threads up until they got metricated in the 1960s. The only old British car I ever worked on was a Vauxhall, and it was basically a Chevy with a smaller body. Whitworth threads have a 60 degree angle just like "normal" threads, but the crest (outside) and root (inside) corners are radiused rather than sharp. A UNC screw will sometimes bind in a Whitworth hole due to this difference, but it is easy to clean the Whitworth hole out with a UNC tap to fix it. No doubt somebody thought the rounded crest and root would make a stronger assembly, but there's no way to cut that kind of profile on a lathe using a simple tool.