Most camshaft manufacturers reccomend .020 to .040 lifter preload. This has bee the standard for years.
So if one looks at the adjuster and it is a 3/8 - 24 thread,
1 turn equals .0416"
So assuming you have a 3/8 x 24 thread 1 turn beyond ZERO lash will equal .0416 of preload.

Hope this helps