It just occurred to me how sneaky manufacturers are. When you buy Playtex nipples, they come in packages of 2s. When you buy the extra retaining rings and caps, they come in 3s. See the difference ?
They pull you into a cycle of buying. You buy a pack of nipples and a pack of rings/caps and you end up with an extra ring / cap so you want to just buy more nipples w/c will bring you w/ an extra nipple. To end up utilizing everything you'll get pulled into buying 3 packs of nipples which will give you 6 and 2 packs of rings/caps which will give you another 6.