172 Planter Part Question

[PVF1799]

While sand blasting I found another part on the 172 Planter that I can't explain by looking at the parts manual. There is this hole in part number PO 27845 that I'd like to know what it's used for to ensure when that I'm using and restoring the tool correctly. I don't recall Dad ever having anything in that hole since we owned it. I tried to make the attached photo clear. Hope it helps.

Ken

[bob in CT]

Not used in mine. Looks like the stop collar is secured with a pin. Perhaps it is an alternative location for the collar for some special application.