These are pre cut zinc engine anodes complete with brass plug and zinc.
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.
E-0 ENGINE ZINC ANODE 1/4"NPT x 1-3/4"
Engine pencil zincs-complete with end plug
zinc pencil length: 1-3/4" diameter: 3/8"
Wrench size: 9/16
plug n.p.t = 1/4"
Picture is of a larger size-for reference