There are different lengths for different applications.
The short barrel spacer can also differ for the same reason, so the two lengths are dependent on application.
How many different aluminium water pump housings did they make with (with different depth hole spacings ) for an la 360, i know about different pulleys and vanes but the bolt spacing and depth is new to me.also which water pump makes a difference, which alternator, ac, Ps etc
hard to find a virgin after 50 years
you can figure out how far you need to go into blind holes or how many threads (turns) you actually need- no need to go longer
going to deep into a blind hole can run into the tap taper and split the casting
you can bottom tap and then count the turns
measure twice cut once