Amazon.com : Premium Kraft Cardboard Mailing Tubes - 4" x 18" - 4" Opening Diameter 18" in Length - Case of 12 Shipping Tubes with White End Caps (4x18) for Art, Drawing,
IN-18 Arduino Shield Nixie Tubes Clock [RGB, USB, Musical] [with Sockets] [ Tubes, Column, Arduino, Power Supply] [Temp. sensor, GPS time sync., IR Remote] [4 TUBES] – GRA & AFCH
2 Pcs 18 inch Inner Bike Tube 18 x 1.75 - 2.4 Bicycle Rubber Tire bike inner tube - Walmart.com
5/8-18 Right Hand Thread Tube Insert for 3/4 ID Tubing – Barnes 4WD
LUXRITE 18-Watt 4 ft. Linear T8 LED Tube Light Bulb 3 Color 4000K 5000K 6500K Single and Double End Powered 2340 Lumens (4-Pack) LR34236-4PK - The Home Depot