I rented a video on the use of the horizontal mill, by Rudy Kouhoupt, in
which he used 1-2-3 blocks in a set-up. So, I bought a set and I'm
confused. There are 3/8 UNC tapped holes in the blocks, but the other
holes are .350. Now, Rudy bolted 2 blocks together by passing a bolt
through the hole in one block into the tapped hole in the other. But
how do you get a 3/8 bolt through a .350 hole? Or, if you pass a 5/16
bolt through the .350 hole, how do you thread it into the 3/8 threads?

The only way I can see to bolt these together is with 5/16 bolts and
nuts through .350 holes in both blocks. But then what are the 3/8
tapped holes for?

Am I missing something, or is this a Chinese gotcha?

Bob