Nickel plated metal thimble standoff. Bell shaped support is 3/8" diameter x .447" overall height.
Reference:
20A-8926 standoff 3/8" diameter x .675" tall
20A-8926-1 standoff 3/8" diameter x .447" tall
20A-8926-2 standoff 1/2" diameter x 1.281" tall
20A-8926-3 standoff 1/2" diameter x 1.187" tall
20A-8866 standoff 3/8" diameter x .687" tall (11/16")

Standoff - metal bell shape

Standoff - metal bell shape .447 inch

Standoff - metal bell shape thimble .447"