Various places on the block are fitted with oil plugs that close off the ends of galleys that carry oil from one part of the engine to another. From the factory these galleys are plugged with press-in plugs. I remove the press-in plugs and had my mechanic tap the holes for threaded plugs.

A freshly tapped oil galley hole at the front of the block (right next to where the water pump goes).

Here you can see the plug and the hex bit used to drive it. I'll be using a soft-set thread sealer called Gasoila.

Plug ready to go into the block.

Driving the plug in.

The plug installed so that it sits just below the surface of the block.