Two of a kind.

I'm a person who likes the number 3. Rarely do I like two of anything, especially in design. I like the odd number, the third wheel, the imbalance. This week I'm thinking and looking at pairs. It's a whole new world.--Rebecca

Single items referred to as pairs:
a pair of pants/trousers
a pair of underwear
a pair of swimming trunks
a pair of shorts
a pair of jeans
a pair of glasses
a pair of sunglasses
a pair of binoculars
a pair of goggles
a pair of scissors
a pair of pliers
a pair of clippers
a pair of tweezers
a pair of tongs

Things that may be considered either one or two items:
a pair of headphones
a pair of handcuffs

Things that commonly come in pairs (two separate items)
a pair of shoes
a pair of socks
a pair of slippers
a pair of boots
a pair of shoe laces
a pair of gloves
a pair of cuff links
a pair of earrings
a pair of contacts
a pair of eyes
a pair of lungs
a pair of kidneys
a pair of wings
a pair of dice
a pair of skiis
a pair of skates
a pair of crutches
a pair of chopsticks
a pair of speakers
a pair of headlights
a pair of windshield wipers
a pair of knitting needles

Note: You can also count pairs of things:
two pairs of pants, three pairs of socks, four pairs of shoes, etc.