The Groove-Genie Model 750 I.D. O-ring Groove Width Gauge makes measuring internal groove widths fast and easy. Extremely valuable tool for measuring the width of o-ring grooves, rod seal grooves or any groove in the I.D. of a bore. Whether you are verifying a new groove dimension or identifying an existing groove, the lathe operator, cylinder repair technician and others will find the Groove-Genie makes a difficult task simple. Easy to use! Just adjust rotating anvil to fit groove being machined and set locking nut. Withdraw gauge and measure with calipers or micrometer. The Model 750 comes with a 3" extension kit for an OAL of 6". Model 750 will fit 3/4" minimum bore and larger. Range: 0.090" - 1.875". Black oxide and zinc plated for corrosion resistance. Condition is New. Made in USA. Shipped USPS First Class.