Starrett 51557 Combination Square Set 12 in 4 Pc

Product Description

The STARRETT 51557 is a 4-piece combination square set built for layout, inspection, and measurement work in mechanical, fabrication, and maintenance trades. The set includes a 12-inch hardened steel blade graduated in 16R increments: 1/32, 1/64, 1/50, and 1/100 of an inch. Three interchangeable cast iron heads attach to the blade: a standard square head, a center head, and a protractor head. Together they handle scribing, angle transfer, center-finding on round stock, and reference measurements without switching tools. At 2.375 pounds, the set is substantial enough for bench use without being unwieldy in the field.

This combination square set is suited for machine shops, fabrication floors, pipefitting layouts, and general mechanical maintenance. The square head supports 45- and 90-degree reference work. The center head locates the centerline on cylindrical workpieces. The protractor head reads angles directly from the blade. Machinists, pipefitters, millwrights, and industrial maintenance technicians will find this set covers the most common layout and inspection tasks from a single blade-and-head system.

Key Features

• 12-inch hardened steel blade with 16R graduation (1/32, 1/64, 1/50, and 1/100 inch)
• 4-piece set includes square head, center head, and protractor head plus blade
• Cast iron heads for rigidity and wear resistance at the reference surfaces
• Interchangeable heads slide and lock anywhere along the blade length
• Center head locates centerlines on round or square stock without calculation
• Protractor head transfers and reads angles directly off the graduated blade

Compatibility

Designed as a standard 12-inch combination square set compatible with replacement blades and heads built to the 16R graduation standard used across combination square systems of this blade length.

Installation Notes

Combination square sets require no power source or installation in the traditional sense, but proper use demands that all locking nuts be fully seated before taking a measurement to prevent head movement along the blade. Inspect reference surfaces for burrs or debris before use, as contamination on the head or blade seat will introduce measurement error. Store the set in its case or a protected location to prevent blade nicking and maintain graduation legibility. Calibration against a known reference standard is recommended periodically in quality-controlled environments.