What is the rule for hyphenating number-plus-noun compounds? Is it six-pack or six pack? Five-iron or five iron?
With number-plus-noun compounds such as six-pack, five-iron and two-step, it is better to use a hyphen. This way you avoid confusion, making it clear that you are talking about a six-pack of beer and not six packs of beer, a five-iron golf club and not five irons, etc.