ToolUSA 6-inch Steel Outside Spring-type Caliper: TZ4506-OUT This Is A 6 Inch Size Outside Spring-type Caliper - Should Choose The Appropriate Size As Needed Open And Close The Caliper With The Tension Screw On The Side - For Comparison Measurements The Tension Screw Is Used To Hold The Caliper In The Desired Position For Measuring You Can Measure Distance, Diameter Or Thickness Of A Particular Item Made Of Durable, Quality Steel And Useful In Many Work And Study Applications