scale sizes for ropes and cables

Not that i know of. Best thing is just to judge it. When i wanted to get some rope for tieing down kit on vehicles, i got a bit of rope from the shed which looked like the sort of thing i would use in the real world and took hold of it to see how it looked in my hand. I then got a couple of sizes of ships rigging thread and did the same with that in the hand of a 35th figure and picked the one which matched.

If tyou can't get hold of the real thing, check photo's and then try and match up from there. I did the same thing for working out the size of concrete panels for aircraft hard standings.

I usually eyeball it like Bish. I have lots of nylon cord that came from parachute shroud lines. That stuff is a good match for the heavy duty tow cables on most 1/35 AFVs. I have also twisted salvaged copper wire (from various electronics) for thinner cables. I'll compare what I have on hand to the kit cable parts to get the approximate thickness. Then of course there are After Market companies that make wire replacement cables of various types for your build. 

Thanks! I love the idea of comparing how it looks in my hand versus the hand of a figure! 

If possably, i always try and compare the real thing and then scale it down. Hope your able to find what you need.

If you find out the prototupe size, it is easy, of course. If you are estimating try to go smaller than scale- cables and such that are oversize look hokey, stuff that is undersize looks better.  However, with anything smaller than 1:48, it is hard to find stuff that thin!

I use some stuff called Beadalon it's a small cable coated in clear plastic and comes in several different sizes. You can find it at Michels,Hobby Lobby,JoAnns.                ACESES5