Brown And Sharpe Mfg Co # 540 3" Precision Machinists Square. The 3" is for the inside angle to the end of the blade and slightly more as per the pictures. It has some stains, a name engraving (many machinists tools do) and a few spots of pitting. The blade sits flat/flush and dead on 90° on my corner reference. A good example/collectors item; please see pictures for details.