John, okay so you got the plastic sleeves from PYI which is where mine came from. Sorry they don't fit your zincs. These have made a huge difference in the way the zincs wear. Previously they wore out at the screws, dumping most of the zinc into the silt below the rudder. Now the zinc actually wears out.
Maybe PYI has the sleeves for the bigger screws?
Karl Andante PSC 34 #276