M21 and M22 position the tailstock. M21 uses Settings 106 and 107 to move to the Tailstock Hold Point. M22 uses Setting 105 to move the tailstock to the Retract Point.
ST10 does not use any settings (105, 106, 107).
Adjust pressure using the valves on the HPU (except ST-40, which uses Setting 241 to define hold pressure). For information on proper ST tailstock pressure, refer to Hydraulic Tailstock and Servo Tailstock.