Fireworks & Pyrotechnics Fiberglass Mortar Tubes Bulk 50ct Case 1.75. Brand: Overstock Central Fireworks. Item Diameter: 1.75 Inches. Set Name: 50ct Fiberglass Mortar Tubes Set. 1.75″ Fiberglass Mortar Tubes 50ct Case Tube Length – 12.5″ Tube Inner Diameter – 1.75″ Set of 50 Fiberglass Mortar Tubes (Plugged) No Base DO NOT USE If your shells are smaller than 1.75″ Firing too small of a shell from too large a tube can cause a low-break, possibly causing personal injury or fires being started. Your receive the wrong item.