Some nouns in English are plural and always counted in pairs even though there is only 1 of them. (Though these items are all single things, they all have two equal parts.):

  • jeans, pants, shorts, etc. (2 legs)
  • glasses, sunglasses (2 lenses)
  • scissors, tweezers, tongs (2 blades/arms)

Some nouns in English are singular but usually come in pairs:

  • socks, shoes, gloves, earrings
  • chopsticks, crutches, skates

Though these items are usually talked about in pairs, sometimes they can be talked about singly:

I bought three new pairs of socks yesterday.

That pair of earrings is expensive.

This sock has a hole in it. (only 1)

I lost one of my earrings.

For a more complete list of things that come in pairs, look here.