The MOST precise extension holders in the industry. The shanks and the inside diameters of these are coaxial and within .0003 concentricity. Measured with a .0001 indicator using a nominal gage pin projected 1/2” from end of the holder. These holders also improve visibility of the tools being used as well as coolant access to the tools. Especially when using smaller tools. Proudly made in the USA by AB Tools, Inc.