Most torque converters have a one-way clutch element that holds the stator below stall speed, and then allows it to overrun at & above stall speed. There are three different types of one-way clutches found in high performance torque converters: roller clutches, sprags, and mechanical diodes. There are also spragless converters (clutch eliminator) which never allow the stator to overrun. See example pictures below to learn about the different types of one-way torque converter clutches.
Example of a stator (courtesy of Sonnax):
Roller Clutch (courtesy of Sonnax):
Sprag (courtesy of Sonnax):
Mechanical Diode (courtesy of Sonnax):
Spragless/Clutch Eliminator (courtesy of Sonnax):
Selecting the type of one-way clutch in your torque converter is dependent upon many factors, including the vehicle's application, power level, etc. Contact a high performance torque converter expert at Automatic Transmission Design today to learn more about the proper selection for you.