Possibly the roll pin is the axle for a roller. Different type of forend attachment?

I thought maybe it had something to do with the rib but I looked at the two vent rib guns I have and there is no pin. Some type of repair to the lug perhaps. Regardless what a wonderful find.

I hope all is well with Meagan.

It appears that those barrels do not have the reinforced forend loop.
Presuming that the vent rib is of the "aftermarket" persuasion, and the gun may possibly have had an aftermarket BTFE.... and knowing that the non-reinforced forend loop might have pulled away from the barrels because of the extra force applied due to the BTFE, which is pretty common... (again, assuming it may have had a BTFE) that pin may have been an anchor point for a rod that went up between the barrels to the top rib to ensure the forend loop would stay put.

Just a crazy WAG on my part.

Assuming that is not a Parker rib, Dean and Richard are probably right about a pin to attach the forend lug to an extra piece of metal that goes into the middle of the barrels and possibly to the top rib.

Guys it has a splinter for end, Gary

I think the thought process was that at one time it might have had a BTF hence the screw in the lug then returned to a splinter. Either way it's a fantastic Parker. I'd love to take it out on the clays course.