Last time I saw one of these we were packing up a marquee section on the big green canvas army marquees. IIRC they were used for bundling the sections up and allowed the strap to be fed around the short end and the long end to be pulled back and act as a tensioning lever.
I was only a cadet at the time, on a summer camp and we were breaking down the marquee we had used as a mess tent.
We had rolled up all the sections and had all these odd looking straps left over from the bag. so after much scratching off heads the duty biff had his moment of brilliance and sussed out what they were for.
The strap looped back on itself through the short shaped end, then you pulled to long piece up and locked it behind the strap and if gave you a locking purchase on the strap.
But as for what they were called, well I stand by my first comment cos we all know how the mod names things