The steering knuckles on my '66 K10 have fill plugs on the backside. Are these for grease, or gear oil? My NAPCO trucks don't have fill plugs there and are packed with grease from the inside.

I'm assuming they are filled with grease, but my step-dad puts gear oil in the front end of his Cornbinder, which has similar fill plugs.

Thanks for the help,
George

1954 Chevy 6400 2-Ton
1955 Second Series Napco 4 x 4 Suburban Carryall
1966 Chevrolet K-10 -- Sold to another 'Bolter