It's about 1.25 inches in size.
Link to Amazon Page for Ives 2A92 Elbow Catch
Oh, and I had one of these from the hardware store for a door to my crawl space, in order to open it from the other side I drilled a 3/32" hole through the "Handle" on the latch and the door and ran a 14ga copper wire through it, then I put a tight loop on each end to keep it from pulling through, when I wanted out I pulled the wire.
In your case I can see this latch being on the inside with the wire sticking out to pull on when you want to open it.
Not so sure this would hold in the bowling balls in the bed of your truck when you mash the go fast pedal to the floor though, but for $3 it would be another cheep fiks.