Originally leather, they were simply for attaching luggage to the carrier, so although part of the vehicle equipment, they weren't truly a 'tool kit' item. They were carried in the tool box though on the pre-pannier bikes.
Thanks for that Rik. I recently found a couple of these straps. Havent seen that style of buckle on any previous webbing ive owned . Into the toolbox they go. Cheers.
According to the few Norton lists I've seen which retained the full additional equipment listings, the straps 'with buckle' measured 42" long by 1" wide (the same dimensions used for both leather and the later (1940 onwards) webbing.
Any chance of a photo of your straps ? Are there any markings on them ?