Timing Chain vs. Gears vs. ?Roller

Factory single chains are flat pcs of steel pinned together. They look like a multi-thicness chain because the are. But the wear surfaces are the edges of the thin plates and the flates of the gears. They are cheap, work, but prone to stretch and even worse for higher rpm work. The "next step is a chain that is basically like a bicycle chain. It's a lot stronger and smother, but they are not strong enough in a single width to really be a performace chain. So they basically pin two sets of links together, making it a "double chain". The cop car 318s and 360s and IIRC 340s had these rather than the link-type single chain.