Update - the problem is not the clamp. On to the next question!
The negative terminal clamp on my battery snapped in half. A friend of mine went to the store for me and bought me a new one, and the one she was sold is a heavy duty zinc terminal. This one.
It's too big, but I jerry-rigged around that. But I can't connect it. When I touch the clamp to the terminal, there are sparks, the terminal is pitted and there is melted lead (I assume from the terminal) dripped down the side of the battery, and the starter motor turns over.
What is going on there? Why is a zinc clamp so different from a lead clamp?
This is the one which broke, fwiw. This is another option for my vehicle. Clearly, I need a new clamp, and I would like to buy one which won't break. That clamp couldn't have been more than a couple months old, three months, tops. The battery and starter motor are also fairly new, maybe from August or September.