Button

[echodog]

It seams to be made of lead I guess it's very big button? Any thoughts? Thanks

 

[smokeythecat]

Big button or child's "whizzer" toy, although those normally have different edges. V's

 

[Breezie]

Yeppers, it's a whizzer! Don't get it knotted up in your hair! Breezie

 

[TheCannonballGuy]

Every "whizzer" disc toy I've seen had something like sawteeth or notches all around its edges, to create the whiz sound when the disc is spun. This lead disc has simple plain edges, so I think it is a hem-weight.