hyphens: numerals and single letters

Hyphenate numerals or single letters and the words they modify:

• e-cigarette
• e-commerce
• e-learning
• S-hook
• T-shirt
• U-turn
• 1,2-dimethylbutylene
• 2,4-D

Note: In the word email, the tendency today is to drop the hyphen. However, the hyphenated spelling e-mail is still in use among more conservative writers and is also acceptable.

Do not hyphenate a compound adjective when the second element is a letter or figure:

• Class II railroad (not Class-II railroad)
• Grade A milk (not Grade-A milk)