Starrett 57S Universal Snug for Surface Gauges, Indicators And Accessories
681-50296 Features: -Universal snug.-With spindle hole diameters 5/16'', 3/8'' (8, 9.5mm).-Gripping hole diameters 9/64'', 5/32'', 3/16'', 1/4'' (3.5, 4, 4.8, 6.3mm).