Business Source 36667 Kraft Clasp Envelopes, 12 x 15-1/2", 28 Lb., Box of 100. Heavy-duty clasp envelopes feature an open-end style, reinforced clasps, and deep gumming on flaps for a secure seal. Metal clasp with rounded edges is plated for rust-resistance. Large flap and superior gumming secure documents inside. 28 lb.