Related Clues:

• SASE, perhaps
• Business letter abbreviation
• Envelope contents: Abbr.
• Env. insertion
• Bus. letter attachment
• Collier's work: Abbr.
• Ltr. accompanier
• Ref. set
• 5 Placed inside: abbr.
• Check inside?: Abbr.
• SASE, for example
• Placed inside a pkg., e.g.
• What's inside an env.
• Ltr. extra
• In this env.