According to our knowledge, D-shaped climbing carabiners are considered to be the most durable and sturdy design on the market. The reason for this is that they have smaller doorways than other shapes, but their doors are still larger than those of oval shaped climbing carabiners, and they bias the load to the stronger, non-gated side, so the smaller, lighter D-shaped carabiners are just as strong as the larger oval shaped carabiners.