What is a 1-2-3 block? You probably remember these gems as one of your first machining projects back when you were in school or during your apprenticeship. 1-2-3 blocks are blocks of hardened and ground steel. They are called 1-2-3 blocks because their sides are 1,2 and 3 inches long, respectively.

Simply put, a 1-2-3 block is a common shop setup tool usually made of hardened steel that measures 1" thick × 2" wide × 3" long. Machinists use the blocks for myriad machine and inspection setup tasks.

A 1-2-3 block is quite simply, a block of hardened steel, that is precision ground to exactly 1” x 2” x 3”. Typically, but not always, there are holes drilled and tapped into the blocks so that they may be bolted together in a variety of configurations for use in the shop.

What Are 1-2-3 Blocks? 1-2-3 blocks are hardened and ground from steel that measure exactly 1” by 2” by 3”. Each side of the block are ground precisely square and parallel to each other. Multiple holes are drilled into them on each face, some of these holes are threaded, typically every other hole.