Officially called shoulder straps, but known to all as L-Straps, this component of the 37 pattern webbing set was used to support the small or large pack on the back and to connect it to the rest of the webbing set. The official fitting instructions gave this description of the pieces:
Shoulder Straps- These are made in pairs, left and right:
Each consists of wide webbing, tapered at the front end, to which is sewn a hook having a side loop carrying a narrow strap, set obliquely:
A removable buckle is provided on the wide portion for connection to the tabs on the back of the haversack:
The other, narrower end, of each L-Strap secured to a corresponding buckle on the base of the haversack:
The ends of each strap end in a brass chape to prevent the webbing from fraying when it is threaded into and out of the buckles:
This pair of L-Straps both date to 1941, but were made by two different manufacturers:
The upper example is marked BH&G Ltd, standing for Barrow, Hepburn and Gale Ltd, the lower example is marked K Ltd. which is a manufacturer I have not been able to identify yet.