High-quality black-and-white photographs of large old machines and tools

[Isambard]

"For those who don't know doing a 3 start *TPI thread you only make the cuts as deep as if you were doing a 24TPI but you must be precisely 120° between starts"

Memory fade Frank?
Thread depth is as normal. However the lathe must be capable of thread cutting at 1/3 of the tpi. i.e 3 start 12 TPI would cut at 4 TPI.