Antique (?) 8" Round HEAVY Perforated Plate/Grate/Trivet??

Can you help me identify this cast iron grate/trivet? It appears to be a trivet for a cast iron dutch oven, except I've never seen one with the "knobs" on both sides. It's also extremely heavy for it's size (7/8" thick at it's thickest point). The perforations are graduated - slightly larger on one side. As shown in Pic #2, it has "2101" on the bottom edge of one side. Any help is greatly appreciated! Thank you!