This is an SPI 30-912-0 81-piece inch steel gage block set, Grade B (working grade), housed in a fitted wooden case with chrome-plated latches and a foam-lined lid. The set covers a range from 0.0500" to 4.0000" and includes blocks in four series: nine 0.0001" increments (.1001–.1009), forty-nine 0.001" increments (.101–.149 plus .050 and .100), nineteen 0.050" step blocks (.150 through .950), and four whole-inch blocks (1", 2", 3", 4"), enabling virtually any measurement combination within range through selective wringing. The blocks are ground and lapped alloy steel with a hardened, corrosion-resistant surface finish suitable for calibration, inspection, CMM setup, height gage setting, sine bar work, and comparator zeroing. This set is offered in new — other condition; the case shows minor cosmetic wear consistent with storage, and one latch clasp is detached but present. SPI (Swiss Precision Instruments) gage block sets are manufactured to ASME B89.1.9 dimensional standards.