The only one I've seen that looked like it would stand any effective use was from the BSA in the late 70's/early 80's. It was single strand wire with teeth formed from the wire. The gauge was heavy enough that it had to be rolled & the teeth were aggressive to the point that you kept the plastic bag it came in to store it & even then it poked through. Does anyone know what their current model is like? All the rest have seemed like they would work slowly (if at all) and were likely to break if you looked at them wrong.