What causes those markings on the bottom of some FX guns?

[OatmealMu]

I've noticed that the blocks of many FX guns often have blemishes on the underside, usually near threaded holes. Mine certainly has them. Any idea what causes this? I was thinking that whatever they use to hang the blocks during anodizing is the culprit. Just curious.

A picture for those wondering.

 

[carlos_hathcock]

Thread locking compound?

 

[Boomerang66]

Yep, I think it is from the anodize process.

 

[DesertSilver]

It's from the screws not being lined up when the person is trying to screw things back together.