They will fit. You have bought cartridges with pads (good), the old single units on the bike can just be removed and binned.
No idea what they are like, but now you have cartridges the next time you just need to buy new inserts, so if you don't like them for any reason it is an easy swap.Ahah!
I saw the little holes and that it was a black cartridge with two slots for screwing the pad in. Now it's obvious it's a single piece.
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Cheers.
Any idea if "Fibrax Science Range" are any good?
No idea what they are like, but now you have cartridges the next time you just need to buy new inserts, so if you don't like them for any reason it is an easy swap.