The extension rods are made of steel tubing, centerless ground. Rods are approximately 3/8" (9.5mm) diameter and have thermal insulators. By removing the hardened and ground anvil ends (end caps) of the micrometer head, the rods may be attached to either or both ends of the micrometer as preferred. Each rod is marked with the length and may be individually adjusted for wear by the hardened and ground anvil at the end. Furnished in case.