The "3" in your picture is not a frame size marking, it is a grade marking. The frame size marking is on the bottom of the rear barrel lug.

IT's getting so now I rarely see an 8 or 10 gauge hammerless Parker I don't like :whistle:

And this one is certainly no exception !

Update 2
 

First thank you all for your replies and kind words. Hopefully this is the correct picture of the frame size. Also I have a picture of the oval metal plate on the bottom of the stock. What is the purpose of this?


Tristan

On any of the guns I have with a plate there or have seen , were typically engraved with initials .

I think I have provided the correct picture now...if not let me know and I will give it another whirl...thank you

Tristan

The frame size of your gun is a #3 as you have surmised .

In regards to cleaning surface crud off metal, use Hoppes #9. Wipe on and let soak in. A soft toothbrush will get the loosened dirt out of the engraving and other crevices. A needle will clean out screw heads. Wipe the barrels down as well. A little elbow grease will do wonders. Don't mess with the screws if you don't have the correct screwdrivers. Someone h as in the past and you see the result.

Beautiful gun. Not too many years ago it would have been considered only fit for hanging on a wall or limited to use with black powder shells. So much has been learned in the last ten years or so about the viability of composite barrels with nitro powders and many of these guns have returned to be regularly used in the field. If you hunt big birds, turkey or goose or hunt in situations where long shots are taken, ducks over big water or crows you will find out just how special a 10 bore is. Do not think shooting a 1 1/8 or 1 1/4 ounce load out of a 10ga is the same as shooting it out of a 12ga, it is not. I am now approaching 1000 birds killed with the short ten, mostly crows and some ducks and geese. I have stood next to another member on here and watched him shoot just as many. The 10 is a significant step up in performance from any 12. As a wingshooter it will give you a lot of "wow" moments. If you are interested in shooting your gun get your barrel walls measured for thickness and if they are in good shape head over to the reloading forum here on the PGCA and start reading all the threads related to loading for and shooting the 2 7/8" 10ga. If you like wingshooting and you haven't used this gun yet you are going to have a lot of fun.

Nice gun! As mentioned, use Hoppe's No. 9, no abrasives! Bronze wool, brass toothbrushes and a brass scraper will take off any rust without removing any remaining bluing or patina. Don't be in a rush. It took decades to age the gun. Don't try to refresh it too quickly! Enjoy!

I still like the edge of a copper penny rubbed on those little spots of rust to level and take them out. It does no damage but will remove the little spots that one finds here and there. Leaves copper behind which just wipes off, but you be the judge. Don't get carried away.