Doesn't sound as if it's critical either way but the UNC has 60 degrees and Whit is 55 degrees so arguably a thread gauge and a magnifying glass might give you the answer. Pity it doesn't have a 1/2" thread as that would give the game away definitively. My milling machine (Taiwanese BP clone) has Whit, UNC and Metric all together, all original. You got away lightly!

Merry

Graham,

Despite the difference in thread angle UNC and BSW (other than 1/2" are interchangeable. This is why the UNC is called Unified. It was to do with standardising screw threads between England ,Canada and the USA in 1949 to avoid some of the problems encountered during WW2. The Unified system did not last too long in this country mostly applied to motor vehicles and agricultural equipment in the 1960s and 1970s.

The unified system produces rather inelegant fastenings with A/F head sizes that are not a fixed proportion of the thread diameter as in Whitworth thread. Strangely no attempt was made to "unify" BSF thread with the ANF series.

Fortunately metrication put a stop to the use of unified threads in this country many years ago.

Eric

Edited By Lambton on 20/10/2013 11:10:21