There is a small group of nouns  that exist only in the plural form, for example:

  • clothes, pants, scissors, shorts, thanks, trousers

These nouns do not exist in the singular form and are usually described as "plural-only nouns".

We use them with plural verbs  and plural pronouns, for example:

  • My trousers are  dirty. I need to wash them.

We cannot use them with numbers.

Plural-Only Nouns with Two Parts

Many plural-only nounsare tools or  items of clothing that have two parts (like trousers , which have two legs).

Clothing

  • panties, boxers, briefs, tights
  • jeans, pants, pyjamas, shorts, trousers

Tools

  • headphones
  • pliers, scissors, tongs, tweezers
  • binoculars, glassesgoggles, RayBans, sunglasses

pair of

Because the above examples have two parts, we can refer to them as "pair of" or "pairs of" to quantify them.

To talk about one item we can say a pair of, one pair of, my pair of, this pair of etc. To specify more than one item we can say two pairs of, three pairs of etc.

  • I need a new  pair of sunglasses.
  • You can get rid of that old  pair of headphones.
  • I'd like to buy one pair of boxers and two pairs of jeans.

Some nouns may be plural-only with one meaning and singular/plural with other meanings. For example, the plural-only noun glasses means a pair of lenses that we wear to help us see better. Do not confuse with the words:
glassglasses ( countable noun): a container for drinking from. I'd like two glasses of orange juice please.
glass ( uncountable noun): transparent material used for windows, screens etc. Be careful not to break the glass.

Other Plural-Only Nouns

  • earnings
  • belongings, clothes
  • congratulations, thanks
  • outskirts, premises, surroundings

In these example sentences notice the use of plural verbs and plural pronouns:

  • Make sure your belongings are  tagged with your name before you check them in.
  • Her  thanks were clearly sincere.
  • If your clothes are wet you can dry them upstairs.
  • The outskirts of Washington are really pretty and they  stretch for miles.

sources : Original Link