1/8" Steel Block Drain Plug (std size for Pontiac blocks), 7/16 Hex Head, Each

The plain block drain plug — 1/8" NPTF male with a 7/16 hex head, one for each side of the block. Seals and disappears, the way Pontiac built it.

These sit at the lowest point of the water jacket, which is also where the rust and casting sand collect, so they are frequently seized solid on a block that has been sitting.

Order two. If the engine is going to get its coolant changed on a schedule, the FSC-135 brass drain spigot goes in the same port and opens by hand.