Hey, what i should have said is i have 1 406" with a flat tappet cam, not a roller cam, the other 3 motors are solid roller cams.
About the .002X1/16" wide flat i grind on the bottom half of the roller lifers lets the oil go down to the roller part of the lifter under pressure just as the .015 hole that Jim mentioned that comp cams now put in their special order lifters, Crower now puts the same .015 hole in the bottom of their brand flat tappet lifters.
I started oiling the rollers yrs ago by grinding the flats on them. As you probably know it's hard to take the roller lifters apart, so the .015 holes are put in the lifters before assy.
I don't have any of those lifters with holes but mine all have flats on them to oil the rollers.
Hope that explains your question.
I'm going up to Ms. around the 20th of June so i will have some hardness #'s to post. I'll take my laptop with me, i'll also take a solid roller cam with me and and roller lifters and get the hardness on them and post the results of all the tests either on this thread or start a new one about this subject. Maybe even post some pics of our shop equipment.
Zip.