That's interesting Asemery, don't think I've ever seen one with such a well turned toggle. You probably know, but the single coloured yarn laid into that rope is known as a 'Thiefs Yarn'. When all ships were using natural fibre rope there was a fair old trade in rope that "went missing" from the Bosun's lockers and got sold to fishermen or other likely customers. The rope makers put a distinctive coloured yarn in their ropes to make them identifiable. For instance, Admiralty rope supplied to the Royal Navy, in Manilla rope there was one black yarn in every two strands, while Sisal rope had one red yarn laid into it. Obviously it was handy if a young Matelot was learning his seamanship too, because it helped identify which was Sisal and which was Manilla. Even today with man made ropes there is a 'Thiefs Yarn' laid into it now mostly for identifying the confusing types like Polyester a Blue yarn, Polypropolene a Brown yarn, etc: in British Admiralty ropes.
In theory it may be possible to trace where your toggle rope came from purely by the 'Thiefs Yarn,' The fact that it doesn't have the two black yarns laid into it as Royal Navy Manilla does, does'nt mean of course that it's not Royal Marine Commando issue, it could well be US Rangers or even British Para's kit.
Thanks for showing us anyway..