To prevent over travel of the lifting screw a stop disc, pin or nut can be fitted to a screw jack that is hand operated.

For motor driven units it is possible for the full capacity of the screw jack or even a greater force (depending on the power of the motor) to be applied against the stop. These stops are called “full power stop nuts”. They must only be used as an emergency device and if such a conditions occurs an assessment made to discover why it happened in order to carry out preventative action. Should the full power stop nut be used at full load in an emergency it might be driven into the unit jamming so tightly that it must be disassembled in order to free it.

It is recommended that external stops are fitted where possible, however they must only be used as a last resort (Note - limit switches are one possible solution to constrain screw jack movement safely - consult Power Jacks for system advice). Under ideal conditions where a slip clutch or torque limiting device is used, a stop pin or stop nut may be used - but Power Jacks should be consulted.

Note that the standard stop disc used on the end of the ball screw on ball screw jacks prevents the ball screw from running out of the ball nut during shipping and handling, thereby preventing loss of the recirculating balls. It should not be used as a full power stop.