The extended lifting screw length is normally equal to the travel stroke. If screw jack is equipped with bellows boot and stop nut, must be added the bellows boot full retract length and the addition stop nut or special closed height. These must be increased the extended lifting screw length. For inverted screw jack, the thickness of the mounting structure must be included. This total extended lifting screw length should be used when determining the permissible buckling load of the screw jack.