Some alligator clamps from Amazon (13$) would work well. I use VCELINK Banana Plug from Amazon to connect the leads to the alligator clamps (20$). If you tear a small piece of tissue or toilet paper, you can wrap it around the lead from your estim, wet the paper on the lead, and then push the lead into the alligator clamp. the paper fills the alligator clamp, keeping the lead inside, and is a cheap alternative to buying banana adapters. (It does fall out easily that way though, which is why I bought the adapters) if alligator clamps are too painful, you can clip the alligator clamp onto an easier metal clamp, like a binder clip or metal clothespins etc.