What the standard defines
Nothing, and that is the finding rather than an evasion. The Arca-style profile is a dovetail in a plate, matched by a clamp that grips its two angled faces. It originates with one manufacturer’s design and has been copied widely enough that the name is now used generically — but no standards organisation publishes it, and no maker publishes a document that another maker could be measured against.
What exists instead is a family of close dimensions. The dovetail angle is consistent enough in practice that most plates hold in most clamps. The width of the plate, the length of the dovetail, the presence and position of a safety lip or a stop screw, and the range a given clamp will close over are all decided by each maker and published by some of them.
What it does not promise
No dimensional match. Two products both described as Arca-style may differ in plate width by a millimetre or two. A clamp with a narrow closing range may not grip the wider one at all.
No safety feature. Some plates carry a lip or a screw that stops the plate sliding out of an open clamp; others do not. The name says nothing about which, and a listing that does not mention one should be read as not having one.
No load behaviour. How much a plate will carry, and whether it creeps under a long lens, belongs to the head and the plate as physical objects. It is not conferred by a profile.
No recourse. Because there is no published specification, an ill-fitting pair is nobody’s departure from anything. This is the practical consequence of the absence, and the reason to prefer published millimetres over a published name.
What it works with
Heads and plates that name the profile, and a good many clamps on cages, sliders and monopods that accept the shape without naming it. Underneath all of them are the two published tripod threads — 1/4 for the camera side, 3/8 for the leg side — which, unlike this profile, are standardised as connections by ISO.
What people ask before they commit
Will an Arca-style plate fit an Arca-style clamp?
Usually, and usually is the honest word. The dovetail angle is close enough between makers that most pairings hold, but widths and the presence of a safety lip vary, and a plate that seats in one clamp can sit proud in another. Because no document defines the shape, there is nothing either maker can be held to — which is why a listing that publishes a width in millimetres is worth more here than one that publishes the name.
Why does this page exist if it is not a standard?
Because the name is used exactly as a standard would be, on both plates and clamps, and a reader comparing two products deserves to know that the word carries a convention rather than a specification. Naming an absence is a result on this site, not an omission.
Last reviewed 12 September 2026