National Envelope Heavyweight 10x13 Clasp & Gummed Envelopes 28 lb. Kraft 150/Box Two prong clasp & reinforced eyelet to resist tearing allows envelope to be used multiple times. Heavyweight 28 lb. Kraft stock for protection & security. Strong adhesion 1 in. high gummed strip on flap delivers a secure seal. Bonus amount - box of 150 envelopes. Heavy-duty one piece box features a reclosable lid with tuck-in flap.