This is a grommet from a Slingerland marching snare.  It is aluminum.  I have three and it is slightly bent on the inner lip and will work just perfect in regards to that application.  It looks like it might polish up better.

Websters definition of Grommet (just thought it was interesting!)

Pronunciation: 'gr?-m&t, 'gr&-
Function: noun
Etymology: obsolete French gormette curb of a bridle
1 : a flexible loop that serves as a fastening, support, or reinforcement
2 : an eyelet of firm material to strengthen or protect an opening or to insulate or protect something passed through it