Abstract: A variable length support column for mounting a seat on a base to form a variable height seat comprises an elongate tube and a rod longitudinally slideable together or apart to shorten or to extend the column;a spring acting indirectly between the first tube and the rod to tend to lengthen the column;a ring of steel balls mounted in bores in tube displaceable to engage against grooves in the rod at any one of different extensions of the column to lock the column at said extension;and a release tube axially shiftable to release the balls into a groove in the release tube to unlock the column.