adapters

Need a little help. The only adapters I can find online for a 4 1/2" to 4" is 4 1/2" to 100 mm. The way I calculate 4" is 101.6 mm. Will a 4 1/2" to 100 mm adapter work for sbp (4") Cragar SS?? Better yet...does anyone have a pair of adapters that will work?