A measuring device includes a transfer sleeve, an assist assembly, and a caliper gauge. The transfer sleeve includes two end surfaces and a side surface; the sleeve defines a transfer hole along the longitudinal direction thereof and perpendicular to the end surfaces, and the transfer hole passes through two end surfaces; the transfer sleeve defines a screw hole along the transversal direction thereof in the side surface and communicates with the transfer hole. The assist assembly is screwed in the screw hole, and includes a screw rod, a spring element, and a ball; the screw rod defines a receiving hole therein; the spring element and the ball are inserted into the receiving hole in sequence. The caliper gauge includes a base plate and two side plate extending upright from opposite edges of the base plate correspondingly.