I don't know what they used on post-war crane cars, but I have a TMCC version crane. Like many, I wasn't careful and the string became tangled when I moved it. After several hours of trying to get it back in place I noticed it was fraying. After some research I bought the stuff in the picture and completely restrung it. It was a pretty good match for color and flexibility, and I think it was a little stronger. I got it from the big online retailer, but I'm sure others have it. One disclaimer, the crane has been sent to a Lionel service center since it no longer responded to commands. I have not actually used the new string since I put it on.