Inner sactum oil galley plug

toolmanmike said
Yes. I used to work in a manufacturing machine shop. You can only drill so far in with a drill and limited to the stroke of the machine and the length of the drill bit. Here comes the step drill procedure. The first hole is say 3/8, then you drill a couple inches further with a 5/16 and then a couple more inches with a 1/4. The last (larger) hole also gives the shavings space to exit the hole.

That's not quite how they are drilled. I work for an Oem big three company and sharpen those drills for a living. Step drills are all one drill of two or three different diameters all drilled at one time.
Multiple redrills of the same hole would cost way too much and take too much manufacturing time.
Step drilled holes are a compromise to reduce cost and not to oil your engine better.