Gold plated steel. The bottom portion of these ferrules fits to a 5/16" hole, the upper stepped portion fits to a 3/8" hole. I measured .312" diameter on the portion of the ferrule that fits into the body, .369" across the lip, .303" length overall. You can mount these flush to the back of the body '50s style or with the upper portion 'above the deck' '70s style. Exactly the same ferrules used on USA Vintage Series Teles and non-tremolo Strats with gold plated parts. Brand New. Genuine Fender 0018876049. UPC 717669612320. Pack of 6.