1 2 3 Block Set
You want a set of these. Seriously. You will use these several times on every knife you build.
Used in layout and setup work. Each set consists of 2 matched, hardened and precision-ground blocks. The squareness on all sides is within .0001" per inch. The blocks are supplied with a plus allowance of .0001" to .0003" to allow nominal lapping. Five 3/8"-16 tapped holes are provided for clamping.
Here's the deal with these. A 123 block is maybe one of the most commonly used and mis-used machinist tools ever. These are commonly used for set ups for filler, to elevate a part or to get parts square. These things are handy as a pocket.
They are called 123 blocks because one they are 1" thick, 2" wide and 3" high.
They are at least half hard. It depends on the manufacture how hard they are but generally to hard to drill with out a carbide drill bit.
Tip: These are AWESOME for use on your drill press. Instead of adjusting your table height all the time, use one of these centered over one of the holes. It will be much easier to hold your work.
Also, have one on your work bench. Pins, pivots and such are often hard to remove in a tight fit up. Use these as punch blocks to tap out the stubborn stuck part with a blunt point punch.
I keep one one on my drill press and one on my bench.
Tip: You can use these as a poor mans file guide since these are fairly hard. Use 4ea long bolts (2.5" long) and bolt them together at the four corners. Open them up just wide enough to fit your knife blank in between. Line the edge of the blocks up where you want your plunge cut you are going to hand file. Tighten up and file against the 123 blocks as a guide.