This is a "Gold Foil" cover for Teisco style pickups, in chrome plated brass.

This is a Chrome plated, brass cover, in the style of (one of the many!)
a Teisco "Gold foil" pickup. Very shallow, and seemingly, a very old
fashioned design - its a specialist piece for a specialist winder!

A Nickel plated steel base for the Teisco Style Pickup

A Nickel plated steel base for the S type Gold Foil cover

Aluminium Pickup Top Plates are typically used on humbuckers with specialist covers, such as H gates, 11 Gates or Open frames - they're a purely cosmetic part really, just something a bit different in terms of the looks for your humbucker.