What is a 2/4 pay out?

[LotusGuy]

I'm still learning about this great old machines and I've noticed that some payouts list 2/4 or 3/5. What does that mean to the player?

I have a couple of the MIlls Chrome fronts but neither have this type of payout wording.

An example from an online auction:

[Sslots]

Due to the thickness between old and new coins they started saying between X and Y amount
So the player didn't get pissed off if under paid.
For example
New coins could be only 2 coins
Where due to wear and tear on old coins it could be 3 or 4 coins

[LotusGuy]

That makes perfect sense! Thanks