ATCO 12" MOWER
I am in the process of restoring a 1947? Atco 12" 2 stroke mower, what I would like to know is the thread on the screws, they look like BSF but they are not,they are not BSW either? what could they be?
AS far as I know, a machine of that date would have BSF and BSW threads, it was not until the 60s that Atco adopted UNF/UNC. However if you are sure that the fine threads are not BSF (or UNF) I suppose that there is a possibility that they are Cycle Threads as used on some JAP engines.
Like Wristpin, I would expect them to be Whitworth. Those on my 1949 12 inch certainly are. In fact I had to buy a set of Whitworth spanners for the job.
Suggest you use a thread gauge on them. Perhaps somebody has changed them over the years?