So that occupancy can be read from the entrance without pushing on every door. A cubicle parked open is unambiguously empty, which keeps people from trying handles and cuts queuing at the door line.

The behaviour comes from the hinge, not a spring. A cam or gravity hinge lifts the door as it swings toward closed, so the weight of the leaf itself returns it to the low point of the track, which is set a little open.

The rest angle is a design choice built into the cam profile. Some systems park at a few degrees, others at closer to thirty, and the two are not interchangeable without changing the hinge.

A cam hinge stores no energy. It converts the door's own weight into a returning force through the slope of the track, so it is silent, has nothing to fatigue and behaves the same on the first cycle and the hundred-thousandth.

A spring hinge stores energy in a coil and releases it, which lets it close a door fully rather than park it ajar, but it applies force to a user holding the door and the spring rate drifts as it ages.

Cubicles overwhelmingly use cam and gravity patterns because parking ajar is the desired behaviour, and because a door that closes itself forcefully is a hazard in a space this tight.

Many can, and that is what the adjustment on an adjustable cam does. Rotating the cam relative to the pivot moves the low point of the track, so the same hinge can rest the door open, closed or anywhere between.

Cubicles for young children are often set to self-close for supervision, and accessible cubicles are sometimes set to rest closed so the door does not obstruct the transfer space.

The adjustment is made with the door hung and the pilaster plumb. Setting it on a leaning pilaster gives a rest angle that changes as soon as the partition is levelled properly.

The bush and the cam face. Every open and close cycle slides one bearing surface over another under the full weight of the door, and in a busy washroom that is hundreds of cycles a day.

Wear shows up as the door sitting lower and further from the pilaster, which first appears at the latch: the bolt starts to catch on the keeper lip. It also shows as a rest angle that has drifted open.

Bushes are usually nylon or acetal and are replaceable on better systems, which is far cheaper than replacing the hinge body and avoids drilling the panel again.

It has to match how the pilaster is restrained. In an overhead-braced system the pilaster is held at the top by the headrail, so the hinge can rely on a pilaster that stays plumb under load.

A floor-anchored cubicle without a headrail cantilevers from the floor, so the hinge and its fixing carry a bending moment into the pilaster, and hinge plates for those systems are longer to spread it.

Ceiling-hung systems reverse the problem again. Fitting a hinge intended for a braced cubicle onto an unbraced one usually shows as a pilaster that visibly moves when the door is swung.

So the door can be removed quickly without tools. In accessible cubicles and in care or custodial settings, getting a leaf out of the way fast can matter more than any other property of the hinge.

The two halves separate when the door is lifted vertically, typically at a specific angle so it cannot happen during normal use. That angle is part of the design and differs between systems.

The trade-off is that a lift-off hinge is a two-part assembly with more tolerance in it, so a door hung on them tends to need its rest angle checked more often than one on a fixed-pin hinge.

By matching the plate footprint and the hole centres before anything is unbolted. The panel is compact laminate and the existing holes are permanent, so the replacement has to land on them.

Measuring is done from the pilaster face to the first hole and between hole centres, not from the outline of the old plate, since several plate shapes share one drilling pattern and several patterns share one outline.

Where the pattern cannot be matched, a larger backing plate that covers the old holes is the usual recovery, and it is worth deciding that before the original hinge comes off the door.