Why do the rockers have different letters/numbers on them?

[Robotech]

I'm merely curious. I did a lifter job on my car and when I look at the lifters, they mostly have different values on them. Its strange. Like for example I have 3 that have a "H X" on them. Here are a few others:

E X
D X
B 7
E 7
H X. *3
B X
Just wondering if anyone knew what the values meant?

 

[rough]

That's a good question! It's not a numbering order that's for sure!

If these are stock rockers google says they are stamped.