I seem to remember when I did my part 1 a few years back our instructor told us it should be doubles as the working lift is made out with singles therefore handrail with doubles then helps to hold the job together.
we have been pulled before by hse for use singles on the stop ends of a handrail, said he want to see double on double do your head in 1 say 1 think 1 say another.
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Just looked at this , surprised as my old gaffer who is the MD of a training centre in Nottingham always told us that this was not the case. Its been said on here a few times you will always learn somthing new , well RJ I hope your reading this thread you cu+t