Two plates can share the same pivot and feel completely different. The spring family and its preload decide the first degree of recline, the knob effort and what year three feels like.
No committee ever published "the" chair-mechanism mounting standard. A handful of bolt patterns and one column taper became one anyway, and they decide whether you can ever switch supplier.
Both let a chair recline. They put the pivot in different places, and that single choice changes seat-pan rise, control feel and cost. Here is how we spec it.
Buyers say "BIFMA tested" like it is one number. It is several, and the mechanism sees the worst of them. Here are the counts we design our plates to clear.
Nylon is cheaper and ships lighter. Aluminium flexes less and survives the fatigue test. The right answer is per chair line, not per catalogue.
The gas cylinder is the cheapest part to downgrade and the one that comes back most as a warranty claim. The class and the stamp tell you which one you are buying.
Most mechanism sourcing pain comes from four numbers nobody pinned down. Get the hole pitch, bore, class and lever side right and the part fits your existing chair.
Three ways to make a five-star base, three different ways it fails. If you know the failure mode for each process, you know what to inspect before you ship.
Loose tolerances do not announce themselves. They show up as a wobbly column, a knob that fouls, a base that squeaks. Here is what to hold and what to inspect.
Got a live spec?
If you already know the component, the target load or cycle class and your monthly volume, the fastest route is a direct enquiry. An engineer comes back with fit, class options and a timeline.