electro-discharge machining (eg. a lifter) ...It uses a tiny wire to burn a passage in conductive metal at the base of the lifter face into the oil galley giving a pressure feed to the face of the lifter so its not just a splash or oil vapor fed. There is no debris in EDM to clean out. Most good rollers are pressure fed in same way, a direct jet onto the roller/cam lobe
Except a wire EDM can only cut shapes out of metal, like a jigsaw. These little holes are put in by a "die sinking" EDM machine with a carbon electrode that slowly burns thru the metal. The holes could/might also be put in by laser.
