The new pole pieces are metric and will not thread into the older bobbins. The original Gretsch pickup designed by Ray Butts used a ferrous pole piece screw that measures 6/40 x 3/4″. The polepiece screw is a Fillister head, slotted, machine screw and chrome or gold plated. Seth Lover who designed the Gibson Humbucker used a 5/40 x 3/4″ screw. The ferrous, Fillister head, slotted, machine screw was nickel, chrome or gold plated. Trying to find 6/40 x 3/4″ Fillister head screws can be difficult to find so I made a run of them for custom pickups and we recently sent a bunch to Jeff Hannah in “The Nitty, Gritty Dirt Band.” Alan Rogan, who works with AC/DC, brought me a bunch so I could duplicate some pickups for the band.