The UIT rail, also known as Anschutz rail, is a standard used for mounting slings and other gun accessories in competition shooting, and is essentially a T-slot track shaped aluminium extrusion profile accepting attachments in the form of T-slot nuts, or similar.
[1] A similar design is called Freeland rail, but the dimensions of Anschütz (UIT) and Freeland rails differ.
[2] The Anschütz rail is wide and shallow,[3] and the Freeland is narrower and deeper.
Accessories made for one of the two types are not necessarily compatible with the other.
Dimensions below are approximate.