The Mahr Federal 4475002 844 NH Self Centering Bore Gage Set; 100-250mm/ 4-10" Range is for measuring the diameter, roundness and conical from of a bore as well as the distances of plane-parallel surfaces. The measuring head consists of a carbide-tipped moving anvil and an interchangeable stationary anvil which has a hardened steel ball; alternatively a carbide ball is available. Transmission lever system transfers movement of the movable anvil to indicating instrument. The broad centering bridge ensures automatic centering in the bore. Insensitive to temperature due to both the shank and transfer rod being made of heat resistant Invar Steel. This gage is also highly resistant to wear and tear due to the carbide tipped moving anvil. Also features a constant measuring force due to built-in spring thus eliminating user influence. Supplied with a wooden case. This model has a measuring range of 100-250mm/ 4-10". Indicating Unit Sold Separately.