A Thread about Threads ....

[simonandjuliet]

Having bought the Lambda , I was trying to get my head around different threads used on older cars and did some research to help understand it - so here's a summary

Please add or correct !!!

The screenshot is a taster, the download is the complete 2 page document

[davidwheeler]

Most of the threads on my Lambdas at least are BSW.      I know this because I have a set of taps and dies that fit.   Vincenzo used BSW because it was designed by an engineer, not a bunch of revolutionary theoreticians in an office in Paris and he reckoned that it was a better engineering job.    I have even installed BSW thread inserts in the blocks for the head studs.   I had it in my head that they were 19/64 ths but in fact they are 5/8 ths

[Tony Stephens]

Many of the Lambda threads, if you study the factory drawings , are as David says, 55 deg Whit form and a tpi pitch (althouh the number of tpi is not, in each case, the same number you would expect from the next nearest Whit size, as engineers chose the tpi for each duty. This can confuse).
The other thing that confuses, and really entertains machine shops, is that these threads are applied to metric stock diameters. So you would get for example 92mm x 20tpi Whit form (rear wheel bearing outer retaining ring), and so on.
Puzzling to all except perhaps Bugatti owners, who  I understand have to have their taps and dies made specially!