Big topic,an-8 push/barb fittings usually take around about 1/2 inch rubber/synthetic id hoses(not that good when some an-8 fittings have an id of about 10mm and so you lose advantage of 1/2 inch hose) but this depends on the manufacturers barb outer diameter,plus you then start getting into cutter fittings, swivel,full flow and ptfe fittings which take different hoses.Manufactures sizes of internal and external dimensions vary even though the threads and what not match.Unless you check out the dimensions of different manufacturers and can mix and match successfully id stick with one brand for all the fittings.Plus anyone not bothered about eye candy aluminium an fittings you can use industrial steel jic 37 degree fittings which are usually far cheaper.Only touched on subject, plenty on net,,no time.