Amazon offers Performance Tool W38137 3/8-Inch Drive Ratcheting Adapter for free shipping with Amazon Prime. 

Product Description:
Converts any breaker bar or sliding T-handle into a ratchet. Hex bolster for use with an open end or adjustable wrench. Works independently as a thumbwheel ratchet. Heavy duty chrome vanadium construction. Oil resistant black phosphate finish. Maximum torque: 164.5ft/lbs (223Nm).