Heyco #SB-625-500 hard black plastic grommet. * Split down the side, it is 11/16" OD, 1/2" ID to fit a 5/8" dia hole. * It is 17/32" long OA with a small flange at one end, and a snap positioned 9/32" back on the shaft. * Sounds about right for a 1/4" thick panel to us.