From PKS

Quick Connect Pigtail w/Stopper Ball – Sold Individually and Color Selected at Random

Designed to be used with Wing leashes for a quick connect and removal from one wing to another. No need to have a leash for every wing, just easily move your leash from wing to wing using the Quick Connect pigtail with stopper ball.

The Quick Connect Pigtail set allows you to have a much larger stopper to ensure that the connection is sure to hold.