True Squares True squares are designed for fast, precision indexing with angle gage blocks. All faces ofWebberTrue Squares are at precisely 90º to adjacent sides,with perfect optical flatness and parallelism to permit use with autocollimators. Applications for fast precision indexing and setting of angular grinding fixtures are almost unlimited. For example: the work and the true square are mounted together on a revolving fixture. A notch is ground by two successive cuts, one at 90º with the true square, and the other at 2º with the addition of two angle blocks (+3º and –1º) mounted on square.An indicator reading is taken before each grind.This process is then repeated by turning the True Square to successive zero readings. True Squares are designed for use as an accessory to our angle gage blocks to easily make angles greater than 45° and through 180°. Webber True Squares also permit a fast, easy check of indexing tables. The gaging faces are at precise 90° angles with optical flatness and finishes that permit the use of autocollimators. The catalog numbers and specifications of our True Squares have been changed in response to updated requirements concerning the application of the uncertainty of measurement. Webber Gage Blocks True Square Specifications Cat. No. TS 21.R TS 21.C TS 44.W TS 66.W Grade Reference Calibration Working Working Material croblox® Steel Steel Steel Tolerances: Deviation From Nominal ±1.0 second ±2.0 second ±5.0 second ±5.0 second Flatness of Gaging Surfaces 6µin. (0.15µm) 8µin. (0.20µm) 14µin. (0.35µm)* 14µin. (0.35µm)* Flatness & Parallelism of Sides 8µin. (0.20µm) 8µin. (0.20µm) 16µin. (0.40µm)* 16µin. 0.40µm)* Squareness of Sides to Gaging Surfaces 6 seconds 8 seconds 12 seconds 12 seconds Area of Gaging Surfaces† 1" x 2" (25 x 50mm) 1" x 2" (25 x 50mm) 5/8" x 4" (16 x 100mm) 5/8" x 6" (16 x 150mm) Surface Finish (Gage Surfaces Only) 0.4µin. AA (0.01µm AA) 0.6µin. AA (.015µm AA) 1.0µin. AA (.025µm AA) 1.0µin. AA (.025µm AA) Estimated Uncertainty of Measurement (K=2) 0.6 seconds 1.0 seconds 3.5 seconds 4.0 seconds Flatness tolerances exclude 1.5mm from the edges on all angle blocks except where marked with *. Then, 3mm from the edge is excluded. † Dimension of gaging surfaces in millimeters is approximate. True Square 401 starrett.com S t arrett -W ebber G age B locks