I assume that you're referring to a standard AN nipple and cutter style hose end? Such as those used with SS braided hose? It's not best to use those as a barb type fitting because they rely on the compression from assembly to seal properly. If it's low pressure it might work, but is not recommended.
I would either get the proper size barb fitting, or try to find a rubber hose that fits both the nipple and the outer collar and assemble it as you would a standard braided line.
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