Product details:

For those occasions calling for a dainty announcement envelope, the A1 (3 5/8 x 5 1/8) is your ideal choice - this diminutive envelope is the smallest of its kind allowed through the mail The A1 envelope is a social and invitation-type envelope; it dimensions make it the most common-sized envelope used for RSVP and announcement purposes. Featuring an attractive square flap, the A1 fits inside all other A envelope sizes.