Blocks, 1-2-3, Ultra Precision

These ultra precision 1-2-3 blocks are ground and case hardened on all sides to 55-60 Rc. They are parallel within 0.0001″, flat within 0.0001″ and square within 0.0001″. They are up to 0.0003″ oversize for lapping.
Each set includes two matched blocks.
The blocks have 23 holes through them. Five are threaded 3/8-16 NC, and the other through holes are 5/16″ diameter.
The set includes a matched pair of 1-2-3 blocks, five 3/8-16 x 1.5″ socket head cap screws and a hex wrench. Furnished in a fitted case.