Each set consists of inside micrometer head and a series of extension pipes of different length, which are hardened, ground, micro-lapped and heat insulated. Satin chrome finished head with positive locking clamp and carbide measuring faces. All sets include micrometer head. Accuracy: Micrometer head stroke: 25mm (1"). Graduation: 0.01mm (.001"). Instrument Error: /-(3qty of rod L/50) mu m. L Maximum measuring length