Some days ago Sam Kowalski, a happy owner of a Boley-Leinen lathe asked me for the dimensions of the collet’s drawbar. He is posting some nice pictures of his lathe restoration in the Old Wood Working Machines forum. Sam, here you have a handmade sketch of the drawbar ;-). Don’t hesitate to ask for more details if needed.
Beware that last informations about Boley Leinen collets for LZ4xx lathes tell that the threading is not M23x1 but a specific thread, say Z23x1, the profile of which is 55º instead of 60º of metric standard.
Take a look at this post about my collets set.