1-2-3 blocks (aka setup blocks) are a highly configurable drill press and milling fixture. They are most useful when you need a straight edge or a fixed support surface. Normal 123 blocks are made of hardened steel ground perfectly square and flat. They also normally cost about 100$ per pair. The block dimensions are 1” x 2” x 3”. The holes (5/16") are used to fasten the blocks to each other or to your table. The usefulness of 123 blocks is enhanced when used along with any of these parts: Setup blocks go along nicely with step blocks (clamp set): http://www.thingiverse.com/thing:50512I printed with hexagonal infill at 35% and they feel plenty strong. You might want to setup up the infill to 50% for the 'clamp for v-block' to make sure it is strong enough for your needs. The clamp uses a 5/16 nut pressed into place. I recommend purchasing a 24" length of 5/16" threaded rod and cutting it into (2)-5" pieces, and (4)-3" pieces.