Check the seat plate bolts and the base before anything else — an unevenly tightened mechanism and a cracked base arm produce the same lean, and one of the two is a safety matter.
Turn the chair over. The seat plate is bolted to the mechanism with four or more fixings, and one loose or one cross-threaded is the most common cause of a seat that is no longer square. Tightening them in sequence, rather than one at a time, often settles it entirely.
Then look hard at the base. A hairline crack in one arm of a five-star base, most often where the arm meets the hub, lets that side settle under load and produces a lean that returns however much you tighten above it. A cracked base is not a thing to keep using: it is the part carrying the whole chair.
If the seat is square and the base is sound, the remaining candidates are a caster that has partly pulled out of its socket and a cylinder not fully seated in the base. Both are easy to check with the chair upside down, and both are more likely than the mechanism itself.
What a fix costs. A replacement five-star base is a standard part: the bases in the chair casters and parts hub read about $40 to $66 on Amazon.com, with the cylinder hole size — usually 2 in — and the caster sockets to match against the old one. A caster that will not stay seated is cheaper still; replacing worn office chair casters explains how to match the stem. If the lean came after a fresh assembly, the assembly order is worth rereading: bolts tightened one corner at a time are the usual cause.
Prices quoted in this text were read on 2026-10-13. The live price is at the top of the page.
Last reviewed 13 October 2026