Range: 5/16" - 6" (8mm to 150mm), 6 pc set includes: 1 gage: 5/16 - 1/2" range x 4.20" overall 1 gage: 1/2 - 3/4" range x 4.40" overall 1 gage: 3/4 - 1-1/4" range x 4.40" overall 1 gage: 1-1/4 - 2-1/8" range x 5.85" overall 1 gage: 2-1/8 - 3-1/2" range x 5.85" overall 1 gage: 3-1/2 - 6" range x 5.85" overall Spring loaded with locking knurled knob Stainless Steel Construction Gage expands in a hole to be measured (locks in place and then removed to determine final hole size using a micrometer or calipers). Get exact sizes of holes, slots, bores, or recesses Rigid handle and double action design (self-centering) for quick checking of inside measurements Constant spring tension for uniform feel Contact points are hardened tool steel and precision ground in the end measuring radius FREE Vinyl pouch included