Keyed Screw Jack
The lift shaft of a translating style screw jack must be attached to something which prevents the lift shaft from rotating. If it is not, the lift shaft (and the load) will turn and not translate. A feature can be added to a machine screw jack to prevent lift shaft rotation. This type of jack is referred to as a "keyed jack" and is available in upright and inverted models. A keyed jack has a keyway machined along the length of the lifting screw. A matching key is fastened to the cover of the jack which will eliminate lift shaft rotation. The keyway in the screw causes greater than normal wear on the internal drive sleeve threads, somewhat reducing jack life.
Ball screw jacks can also be supplied with a device that prevents rotation of the lift shaft. Anti-rotation is accomplished by a square guide attached to the screw translating inside a square stem cover attached to the jack. The square stem tube is supplied with lube fittings.
In this road barrier application (See Image Below), the linear motion is provided by an inverted keyed machine screw jack.
