I was at a barn today and had a chat with another farrier about traction, it started when he was drilling and pinning a pair of shoes. He put a pin in each heel, I commented how much better I thought pins were, he related that at this barn he found that more than 2 pins per shoe gave less traction than 4 pins, his reasoning was from experience, with 4 pins the horses slip and slide on the concrete isle ways,because the concrete has been worn so much that the rock/stone/aggregate is exposed, thus not allowing the pins to sink in and grab. I m passing it on for consideration. ray