We, too, just bought two of those pins just in case we should lose one.
Funny story. We decided to remove the torpedo-shaped gizmos that accept the fingered portion (note my use of scientific terms here) of the Aventa tow bar. When we got to our present campground I removed one and then got distracted. Today, Sandy had a panic attack and informed me that someone has taken on of the gizmos overnight.

Fortunately, I remembered that I was the culprit. We both breathed a deep sign of relief.