They are used as a reference for calibrating measuring devices used in machine shops, such as micrometers, sine bars, calipers and micrometers (when used for inspection). Gauge blocks are the main means of standardising lengths used in industry.Product Details:Package Included:-2 pieces 4 x 10 x 100 mm- 2 pieces 4 x 14 x 100 mm- 2 pieces 4 x 18 x 100 mm- 2 pieces 4 x 22 x 100 mm- 2 pieces 4 x 26 x 100 mm- 2 pieces 4 x 30 x 100 mm- 2 pieces 4 x 34 x 100 mm- 2 pieces 4 x 38 x 100 mm- 2 pieces 4 x 42 x 100 mm- 1 x Wooden Storage BoxTips when you use them:To use them, the blocks are removed from the set, cleaned of their protective coating (petroleum jelly or oil) and screwed together to form a stack of the desired size. The blocks are calibrated accurately at 20 C (68 F) and should be kept at this temperature when measuring. This mitigates the effects of thermal expansion. - blocks, made of a harder substance such as tungsten carbide, are mounted at the ends of the stack wherever possible to protect the gauge block from damage during use.