Jack post
steel post used in the construction trades for temporary support of ceilings, walls and trenches
A jack post (screw jack, telepost, adjustable steel column) is a steel post used in the construction trades for temporary support of loads such as ceilings, walls, and concrete formwork, and as shoring in trenches. They are designed to be able to mechanically telescope to about twice the distance between their pre-drilled adjustment holes. Most examples use removable pins for coarse adjustment and a jack screw for fine adjustments, but many variations exist.
Terminology
Although jack posts are widely standardized, their terminology is not. "Jack post" is just one of many describing the same system: others include any assortment of "adjustable", "steel", "screw", "jack", and "shoring" with "post", "column", "jack", and "prop", depending on region, trade, and precise construction. The "jack" refers to examples with a jack screw to adjust the precise length of the post. They are also known by any number of proprietary names, notably "Acrow prop" in the U.K., after the Acrow Group that introduced them in the UK.
Description
Jack posts are telescopic tubular steel props consisting of two primary parts, both tubular: the main body of the post, and the threaded jack screw or other adjustable fitting on one or both ends. Both ends are normally fitted with flat metal plates on the end, increasing their bearing surface. A recent improvement to Acrow props was to shape this baseplate with notches, allowing pallet loads of horizontal props to be stacked neatly, rather than randomly piled.
Gross adjustment for length is first made by sliding the two sections within each other until they almost fill the gap, inserting a pin through regularly-spaced pre-drilled circular holes to lock them together, then adjusting the screw to the degree of tightness desired.
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