Alvin Black Knight Storage Tube 4 and 1/4 inch Inner Diameter. Made of durable black plastic, this tube is water resistant, so you can be sure that your documents do not get wet. And a nice large diameter so the roll up is not so severe. Expands from 30 to 45 inches in 14 locking increments with a 4 and 1/4 inch inner diameter. Comes complete with a removable adjustable shoulder strap. A nice tube for the money.