Ding, ding, ding..... you found it UB.
Here's a pic of one, though not good, shown where it is used. If the page doesn't open where it's at, you would be better off scrolling up from the bottom and looking for S7664 Parachutes? Skydiving equipment? Shop ParaGear.com!
It is used when packing the reserve, so only a rigger would use one and probably most of the people that jump wouldn't know it if it banged them in the head repeatedly.... YT.....
A pull up cord is inserted through the closing loop of the container, and threaded through the four grommets on the closing flaps after the reserve chute is in place. Then the cord is wrapped around a T handle. The plate is layed on the top grommet and protects the container when the T handle tightens up the closing loop, right before the pin is inserted. A rigger kneels on it to help compress the parachute and expell any air. The Y allows enough room for the pin to be inserted, but the slot is narrow enough to rest on the grommet.
You're up Bob