The Twist Panic Snap is a very popular snap used by Parelli and recommended by other top horse trainers. They are ideal for lead, training, and lunge/longe lines.
It has the ability to be released if needed in a panic situation by twisting the center mechanism.
These high quality snaps are a bit on the pricey side and not usually available in tack or feed stores.
They are available in your choice of stainless steel or brass. Overall length is 4 1/4" and ring end inside diameter is 1".