Business Source Heavy Duty Clasp Envelope - Clasp - 3 3/8" Width x 6" Length - 28 lb - Clasp - Kraft - 100 / Box - Brown Kraft - Heavy-duty clasp envelopes feature an open-end style and metal clasp with rounded edges. Metal clasp is plated for rust-resistance. Flap offers superior gumming to secure contents. 28 lb.