#0016, 4 inch Digital Caliper: Sometimes kit parts can be similar in size and a ruler just won't do. To get an accurate measurement you need a caliper. This 4 inch digital caliper is made of stainless steel and can give you accurate outside, inside and depth measurements. The digital read-out is easy to read and by the push of a button changes your measurement from inches to millimeters. Two button batteries are included. Get them while they are available at this low price.