Originally Posted by TranquilTempest
The 'F' in the second section is what tells you it's the lower force spring. That's not determined by the longevity rating.
First of, I made a mistake: The MX518L uses 20m rated ones, not 50m.
Secondly, NOPE, you are WRONG. The difference is in quality / manufacturing. The new D2FC-F-7N(20m) used in the MX518L have a different model number.
Left: new model used in the Legendary, hard and loud. Right: old model used in the G400, fainter and smaller letters.
Likely from a different factory or they changed manufacturing processes. Either way, look for omrons where the letters look like on the right, thinner and more faint.
Alternatively, I assume the number represents batch? So look for a lower number aka earlier batch.
Imo the best switches were the ones used in the original MX518, which I think were 5m rated. They are just called D2FC-F-7N without a rating in the name.
So those are the ones I would buy. but "old" 20m rated ones will do fine too. I wouldn't bother with any other switches, these are the springiest and most pleasant to rapidfire from my experience, low travel time, spring back fast, quiet, seem to go well with the shell.