Mountz 060064 Wheel 4" (1/4 & 3/8 Male Sq Drive) (+/- .002; 4 inch)

Input driver: 1/4" & 3/8"
Tolerance: +/- .002
Radius: 4" 
Weight: 65 lbs

datasheet

FEATURES:
Calibrated Dead Weight are the official means by which torque analyzers and torque sensors are calibrated and are traced to National or International Standards, such as N.I.S.T, ISO and others.
Many industries like as medical, aerospace, nuclear and others continuously calibrate their measuring equipment to comply with government regulations. For companies that prefer to have calibration capabilities in-house when their calibration requirements become extensive, they need calibration equipment.