Snap hooks or Carbine hooks as they are sometimes known, are generally used for tethering rope. The gate can be opened by one hand. It automatically shuts when released. Sizes of 3mm,4mm,5mm,6mm,7mm,8mm,10mm,11mm,12mm are available. These represent a length of 30mm all the way up to 120mm long. Carabina hooks like these are also available in a wide opening style, where the gate opens more than those shown below.