It's 1/4" and 20 tpi no matter what you call it. The only difference is the core diameter. 0.186" for UNC and 0.1887" for Whitworth.
Originally Posted by Nicholas Lindan
The British Standard Whitworth thread was specified in 1841. During WWII there were compatibility problems with various British, US and Canadian thread standards which lead to the UNC and UNF threads being adopted in the US in 1949.
There were cameras in existence before 1949 with 1/4" 20 tpi tripod threads so I suspect that they were Whitworth.