Er, wot it says on the tin, really.
Made by Fulton of Bisley, it's a milled blued steel Weaver rail that attaches to the Enfield No4 action, enabling any type of scope to be fitted to the rifle.
Uses rifle's existing ladder sight fixing screws at the back and an integral cammed gripper piece, resulting in a very robust solution that, when I used it, simply did not lose zero.
Has a very minor spots of rust at the front, so could do with being rubbed down and re-blued, phosphated or painted. Otherwise it's 100%
I also have two pairs of Weaver rail scope rings. A pair of Fulton-made for 26mm scopes and a pair of genuine Weavers for 1" bodies.
£35 the lot including postage.