3/4 DIA X 2 PENCIL COMPLETE ZINC PENCILS WITH PLUG According to the Manufacturer ZINC. Size 3/4 x 2 UNC 1/2 Plug 3/4 NPT Material: Zinc Alloy - For use in Salt Water; - NOT recommended for use in Fresh Water; - Alloy is manufactured to meet or exceed U.S. Military Specification (US Mil-A-18001K) Don t be fooled by claims that only one alloy will protect in all water environments. Only MARTYR Anodes offers you the choice of the right protection for any application! You are bidding on a Brand New Item. We are a full service Marina with over 700 slips. W.