Arca Rail
Also: Arca-Swiss
A tapered dovetail clamping standard, borrowed from camera tripods, that lets bipods and tripods slide and lock anywhere along the forend.
The Arca rail is a dovetail profile originally designed for camera quick-release plates that has been widely adopted for precision rifles. A matching clamp grips the tapered sides and can lock at any point along the rail’s length, so a bipod or tripod head slides fore and aft to balance the rifle and then clamps down solidly. Compared with fixed sling-stud attachment, this freedom of placement is a major reason the standard caught on with field and competition shooters.
An Arca rail is most often run along the bottom of the forend, either machined into the chassis or added as a separate length of rail. It complements rather than replaces the m-lok and picatinny-rail systems used elsewhere on the gun, since each serves a different role: Arca for sliding support gear, the others for lights, sensors, and accessories. The continuous clamping surface is what sets it apart from the discrete slots of older patterns.