All Simmons Pads, except one of the very early SDS5 Series, use pipe
diameters of 22mm, that is 7/8 inch. So Pearl hardware is the first choice,
but will cost you an arm and a leg. There are many no-name products on the
market, doing the same job, because the pads are really not heavy. 7/8 inch
is a standart diameter for water installation in buildings. You can
construct your own custom rack with this material for nearly nothing, if a
friend of you is a plumber. But your roadies will kill you :-).