I got a 125Amp panel (Siemens) for installation, and found that the cover screws included did not fit. I later found that my sheet metal screws, fit perfectly. Are there any NEC guidelines against this?
That self tapping screw is a code violation and I know several inspectors that will fail a home owner and an electrician for not using load center cover screws.
The load center screws have a larger head and almost always have a #2 square / slotted head , I got hammered many years ago and even stock several different brands as they are different.
Many of these screws are self forming NOT self tapping. Code specified self forming 2 threads in contact, yes self forming are tough to put in the first time but believe me that is a red flag for inspectors in my area.
I believe 1 brand has corse threads but it is a large head with a slotted / #2 square drive and is ok because it is according to the mfg directions. Self tappers do not.