Bore and duty. A curb box is a narrow shaft — commonly around two and a half inches — over a small service stop, and it is operated with a long key rather than reached into.

A valve box on a main is much larger, over a valve with a substantial operating nut, and sits in the carriageway rather than the footway.

They look alike in a catalogue photograph and are not substitutes: a curb key will not reach a main valve, and a main valve box over a service stop is an unnecessary hole in the footway.

The isolating valve on the service line between the main and the property, usually at or near the boundary.

It is the valve used to turn one property off without affecting anyone else — for a repair, a change of occupancy or non-payment — so access to it matters commercially as well as technically.

The box exists solely so that stop can be operated from the surface without excavating a footway every time.

They are small, they sit in footways that get resurfaced and landscaped, and there is no obvious cover to notice — a curb box lid is a few inches across.

Once buried under a new surface, the only way to find it is a record drawing and a detector, and neither is reliable at that scale.

Marker discs, accurate records and raising boxes during resurfacing are the practical defences, and the cost of not doing it is an excavation per property.

A long-reach curb key sized to the stop below, and the fit matters: the stop has a specific operating head and a key that nearly fits will round it off.

Because the operator cannot see what they are engaging, a key that slips is often not noticed until the head is damaged and the stop can no longer be turned.

That is why key type is worth recording alongside the box, and why crews carry more than one pattern in areas with mixed historic fittings.

Yes, and it needs to be more often than a main valve box, because footways are resurfaced frequently and by different parties.

Screw and slide adjustment work the same way as on a larger box, at a smaller scale, and the same limits apply to how far it can be extended.

Because the shaft is narrow, a curb box that is extended too far becomes a long thin tube that fills with debris and is awkward to clear.

A lid that seats properly and a base that closes reasonably around the stop. A narrow shaft blocks with far less material than a large one.

A blocked curb box is effectively a lost curb box: the key cannot pass, and the only options are clearing it out from the surface or excavating.

Some designs include a plug or a debris cap below the lid for exactly this reason, which is worth having where the box sits in a soft verge.

Usually less, because it lives in a footway or a verge rather than a carriageway — but footways are driven over more than people admit.

Vehicle overrun at driveways, delivery vans and parked cars all load footway boxes, and a lid specified for pedestrians alone will fail there.

Specifying for occasional vehicle overrun in any footway near a crossing or a driveway is cheap insurance against a broken lid and an open hole.