Marine engine zinc anode for all Caterpillar diesel engines. Zincs should be replaced every season or after 2/3 of zinc has eroded, which ever happens first. These are pre cut zinc engine anodes complete with brass plug and zinc. E-2 ENGINE ZINC ANODE 1/2"NPT x 2" Engine pencil zincs-complete with end plug zinc pencil length: 2" diameter: 5/8" Wrench size: 7/8 plug n.p.t = 1/2" Also workd for Cummins B Series: C Series: QSM Series: Cummins 68241 GM and Detroit Diesel-8517479 Yanmar-119574-18790 John Deere RE54993 Picture is of a larger size-for reference