Machinists use 1-2-3 blocks for setups, layout, and inspection. These blocks are hardened steel. They are ground to extreme tolerances, often within 0.0002 inches of their nominal dimensions. They contain holes that are threaded or cleared. This lets you bolt them together to build custom fixtures. In automotive machining, they help align engine heads or blocks on the milling table. They ensure cuts are perfectly square to the reference surfaces.
Mechanic Glossary
1-2-3 Blocks
Precision-ground steel blocks measuring exactly 1 inch by 2 inches by 3 inches, used in machining and layout work for calibration and setups.
Frequently Asked Questions
Setting up precision measurements, checking deck flatness, and securing parts on a drill press or mill.
The holes allow you to bolt blocks together, clamp them to machining tables, and reduce weight without losing strength.
Yes. High-quality blocks are hardened to around 55-60 HRC to prevent wear and maintain accuracy over years of shop use.