BUSCH PRECISION Steel Parallels are a most essential tool for the toolmaker, machinist and inspector. Normally sold and used in pairs, steel parallels are indispensable for setting up and checking work. Made of high quality alloy steel scientifically hardened for stability and wear resistance, BUSCH PRECISION Steel Parallels are precision ground on all four sides. Ground to 0.0002" in size, parallel to 0.0001" in 6" and ±0.020" in length.