A simple old Finnish army sling, meant to be used with the M39 rifle, but works equally well with whatever gun you can fit it on - the army used these for every weapon model. The maximum length is 110 cm, width 2,5 cm (1").
If you need a really solid and basic sling for your rifle, here's one. These are Finnish made, which means they will probably outlast you, even if you're tough as nails. The free end is weaved through the rear sling swivel and adjustment buckle, then through the front sling swivel, folded over and attached to itself with a metal stud.
These are gray or grayish green in colour.
Most seemed unissued, some slightly used, all in excellent condition. These are not very common any more, we suggest grabbing one... or a couple.