abbreviation for "fragment"

Greetings,

Apologies in advance for the rudimentary question. I’ve noticed different scholars using “fr.” and “F” as abbreviations for fragments. Are there conventions for which to use for which ancient authors/types of fragments, or is it a matter of picking one and staying consistent? In the case of “F” how do you make it plural (for “fr.” I’ve seen “frr.”)?

Many thanks for shedding light!

fr. is standard, plural frr. It’s usual but unnecessary to leave a letter-space between fr. and the numeral.

F (no plural) is used only when citing editions that use it, if then.

Thank you!

I understand that fr. and frr. are standard, but I’m still not entirely sure when to use F or why some scholars choose to use F instead of fr.

For instance, it seems that the FGrHist consistently uses F, never fr. So when I reference a fragment that I found in FGrHist do I need to use F instead of fr. when I refer to the fragment?

Thanks again!

A quick follow up:
For Diels-Kranz it seems like fragments are never referred to with fr. or F, but simply (e.g.) DK 11A9… I wonder why not using fr. became the convention of the presocratic fragments…

Diels-Kranz has its own, unique, universally used, numbering system.