GearWrench Brake Resetting Gauge Features and Benefits: The diameter range is 6-1/2" to 14-1/4", calibrated into 1/32" (1mm)increments Sets the proper clearance between brake lines and drums The tool has a locking knurled knob to keep measurement accurate This quality tool is used to set the proper clearance between brake lining and drum prior to assembly. Inside calipers measure drum diameters and outside calipers transfer measurement to brake shoes. Knurled know locks tool at measurement. Working drum diameter range: 6-1/2" in. to 14-1/4"". Calibrated in 1/32" in. (1mm) increments. Warranty: Lifetime warranty does not cover abuse