Maintenance standards require that all rivet be no less than 2 diameters (2D) and no more than 4 diameters (4D) from the edge of the sheet, with the optimum distance being 2.5 diameters (2.5D). This tool will accurately gauge the distance of rivet holes from the edge of the sheet to verify that they are within these standards. Simply slide the tool against the edge of the sheet and verify that it aligns with the centerline of the rivet holes. You can also use it to establish the ideal centerline by the same technique. One side gauges distances for 1/8" (-4) and 5/32" (-5) rivets, and the other is for 3/16" (-6) rivets. Overall dimensions: 3" (76mm) long, 1" (25mm) wide, .125" (3mm) thick. CNC machined in the USA from aircraft grade aluminum.1 lbs (0.5Kg) shipping weight.