It's about the same size as the obscured lanyard ring picture. I'll just spoil it so someone can post something better ;)
It's the bolt of an SVT, showing through the notch in the rear of the bolt cover ;)
Same rifle as the one in the site banner.
Printable View
WW2 era US 1903 Springfield & M1 Garand Rifle Grenade Recoil Rubber Stock Boot ;)
OK, here's one...