Snub Lead - for Off Lead training - 19mm wide 10 to 12cm long, small snap hook
 
Extremely useful in Agility Classes - something to hold your dog, or direct it to objects and yet it won't get in the way over jumps or in a tunnel. 
 
Adds weight - to replicate the feel of a lead on the dog - useful when first starting Off Lead training
Gives you something to grab if required
Particularly useful for long haired breeds
May not be as appropriate for very small breeds as the lead may drag on the ground