A hyphen is different from a dash, which keeps words apart. A dash (—) is usually longer than a hyphen but is sometimes shown as a hyphen with a space on each side. This means that the two punctuation marks are often confused.

Example:

Light - reading

These words are not connected. This does not mean “light reading”. It means “reading light”.

The examples that follow show how to use hyphens to connect closely related words:

1. Terms that have two or more words and are adjectives before a noun:

low-altitude flight, high-pressure chamber, air-conditioned compartment, transmitter-receiver system, quick-release fastener, clamshell-type flap, eighteen-inch monitor, cast-aluminum bracket, three-to-one ratio, trial-and-error method, air-to-air refueling, soap-and-water solution, up-to-date information, run-on torque, break-away torque, cut-in speed, in-flight entertainment system, stiff-bristled brush, fire-resistant material, self-sealing hose

2. Two-word fractions or numbers:

forty-seven, ninety-ninth, one hundred and sixty-two, three-sixteenths, one thirty-second

3. Terms that contain a capital letter plus a noun, or a number plus a noun, and that usually describe the shape or configuration of something:

L-shaped bracket, O-ring, T-shirt, U-beam, Y-coupling, V-band clamp, 3-prong connector, 180-grit abrasive cloth

4. Verbs that contain a noun or another part of speech as the first element:

die-cast, arc-weld, fusion-bond, stop-drill, vacuum-pack, heat-treat, jump-start, air-condition, short-circuit, fast-forward, cold-roll, dry-clean, blow-dry

5. Terms in which the prefix ends with a vowel and the root word begins with a vowel:

de-energize, pre-amplifier, de-ice, anti-icing, pre-engage