What's this screw for?

[Wilmurt]

What is the purpose of the screw on the end of the dolls head extension on a Parker Repro? Is it just there to hold the dolls head in place? The dolls head extension on my 16 gauge Galazan barrel is not a perfect fit (open space is less than 1/8") and its not engraved like the barrel in the photo here (pirated from GB). The gap is somewhat unsightly and the un-engraved extension looks unfinished. I'm thinking of getting a new extension made to fit and also engraved like in the photo. It would be a simpler job if the screw just removed the dolls head without messing up anything else. I don't have a photo of my particular barrel end showing the screw so I pirated this one from GB. Gun locks up tight and have not had any firing issues.