When the two outside jaws are closed, the nib width is smaller than the dimension listed. To measure the smallest measurable inside dimensions, the jaws must be opened, leaving a space between the jaws. All MITUTOYO Vernier Calipers meet or exceed Federal Specifications for accuracy. Machine divided and engraved from master for extreme accuracy. Made of hardened stainless steel throughout, ground and lapped for accuracy. Scale surface is satin-chrome finished. Raised sliding surface prevents defacement and wear of graduations. Long 50-division vernier scales have wide spaced easy-to-read, clear, crisp graduations on satin-chrome finish. Easy wear adjustment of vernier scales.