SPI Half Base Depth Micrometer Half base permits measuring depths of holes and slots close to shoulders and in between obstructions. Quick reading graduations. Features Include... 0-6" Measuring Range 0.001" mm Graduation Rods: 6 Base Width: 2.25" Rods are precision ground and lapped Rod Diameter: 0.177" Ratchet Stop Certificate of calibration Furnished in fitted case