Mini-Rocket: Mini Pipe / Diameter Caliper and Ruler - Fractional &ndash; Black Anodized Aluminum Mini pipe diameter caliper. Measures outside pipe sizes up to 6.5 inches in diameter. Unique design with a 4 inch ruler on one edge. Tapered swing arm measures interior pipe diameters up to 1.7 inches. Conversion chart from outside diameter to inside diameter printed on the caliper. Item is made from an incredibly durable black anodized aluminum.