222K Featherweights had three different throat plates.
Most of the earlier 222K machines had a chromed throat plate with markings 1/8" apart and the markings marked in fractions of an inch up to 3/4".
Later 222K machines started having chromed throat plates that had markings 1/8" apart but the markings were labelled 1 to 8. This allowed seam guides up to 1" rather than the 3/4" on the earlier plate.
The third version of the 222K throat plate is similar to the second version in that it has markings numbered from 1 to 8 but rather than being chromed the plate was anodized.
White featherweights had similar anodized throat plates with the same markings.
The anodized finish is more scratch resistant than the chrome finish.
The anodized plate was used on the later red "S" badged machines but not all red "S" machines had the anodized plate.
It almost seems that in the last few years of production Singer had bins of the three types of plates and they just put whichever plate they wanted to onto the machines in order to use up the plates that they had in stock. There doesn't seem to be much rhyme nor reason as to which throat plate went onto which machine, aside from the earlier machines which all had the chromed plate with markings in inches.