Got some 6mm black from bells of hythe called asasin heavy draw and not very stretchy, the squares you get today are not as good as the stuff we used as kids, that stuff seemed to be a lot more stretchy, the stuff you want is linatex was used as conveyor belt rubber in the pit, is a pinky red colour, is cut from sheet/ two edges were smooth the other sides were textured, used to come on the sam stanley catapults, have you got yours on a milbro mate?