I'm not sure what you mean by the holders, I'm not very good with bike terminology
But I only noticed that the damn thing was missing today, so I've no idea how long I've been riding without one of the nuts.
I'm guessing a week though, because it has been a week that my front wheel (when un-folding) has been making a noise as it touched the ground.
I'm also thinking of replacing my chain, but have no clue which to get, apparently there are many different types
I have 6 speed Brompton 2011, but even then, there are 2 to 3 options according to
this Brompton page.