Vintage Horticultural and Garden Machinery Club

If only one head stud is damaged I would suggest using one of the others with a good thread to establish what the thread is. I have only worked on MK10,12,15 and 25 Villiers engines.

At some point in the Fifties British Industry went American, Whitworth, BSF, BA, CEI and a host of other specialised threads went and all new designs were required to have UNF/UNC. This led to the Mini range and some others having engines with BSF/Whitworth types and chassis fittings, having been designed in 1957, using UNF/UNC threads. Then in 1973 it all changed again and we went Metric. Having said all that the one thread in use all over the world to this day is ¼ Whitworth. It is found in the bottom of very camera ever made and on every tripod, good old Joseph Whitworth, specified it in in 1841 and it led to the first National Standards in the world, British Standards. Seems a bit appropriate to be writing this on the day when Britain has left the EU! Not that we’ll abandon the metric system now.

the one thread in use all over the world to this day is ¼ Whitworth. It is found in the bottom of very camera ever made and on every tripod

It has always struck me as strange that the square drives used in socket sets made in “metric countries” are quoted in quarter, three eighth and half inch sizes etc. They appear to be another accepted international standard for that application.