Thanks @Dezcom
I was searching the forum for numeral metrics which is why I couldn’t find any info. For any other newbie that lands here I should have been looking for proportional vs tabular figures.
Glyphs tutorial: https://glyphsapp.com/tutorials/figure-sets
Forum topic: Tabular figures // period, comma,
Monotype article: https://www.fonts.com/content/learning/fontology/level-3/numbers/proportional-vs-tabular-figures