IRON MILITIA/HORSE PLATE? Help needed with this toughie!!

[36coupe]

Need help id-ing this IRON disc 2.75 inches. Reverse side does show some attachment business. Found on an early site with some early Upper Canada coins and glass and pottery shards near the road. Item found at back of the field. Also found at the back early Irish hunting button and button with British crown and anchor. Any help here much appreciated.

 

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[Ant]

I see a stars and part of an anchor above it at the bottom, and a screw post on the back, it is military related IMO.

 

[Ant]

Now looking at it on a monitor I don't know. Is that an arrow or part of an anchor above left bottom center, left of what looks like a star?