The gas mask strap was used throughout the war on any type of German box.
Price per set for one gas box. The set consists of a long strap with a buckle and a peg, a short strap with a hook and a peg, and the smallest for sewing on the lock of the tank (with a thread for sewing).
Straps are assembled by hand, the loops are overstiched on a special buttonhole machine. We used a specially selected thin strap of pale green color (cold shade). The strap is woven of natural thread. On cheaper copies they often use a thick sling (dog leash) of khaki (yellow-brown) colour, that is incorrect.
Steel hooks without stamps (made after the war on the same equipment in Germany); original ones with stamps may be also found. The same can be said about buckles. Pegs are recently made of steel. Authentic ink stamp "H.R.E. 35" or "H.R.E. 41" on the inside of the strap.
There is a common misconception that straps must necessarily have leather tips and spacers, and that such straps are "early", and they must be worn with an uniform at the beginning of the war.
In practice, completely cloth straps (as here) were more common, and leather-reinforced ones were produced (judging by the preserved samples) from 1940 to 1942 as an option. Later (since 1944), the "reinforced" version was introduced with rubberized tips instead of leather ones.
Read the article at the link.
There are a number of examples of the use of straps with gas mask boxes produced in different years. Spoiler: There is no uniformity.
The straps differed both in color and in the thickness and structure of the weaving of the sling. The only thing the Germans didn't have was straps made of thick (reinforced) slings, which are now used to make leashes for dogs. German straps were usually thin and light.