Alvin - Plastic Telescoping Tube - 3 Inch Diameter - The Alvin Plastic Telescoping Tube as a Friction Lock. These telescoping tubes adjust in length from 27 inches to 50 inches with a 3 inch inside diameter. The Friction lock adjusts for desired lengths. Alvin Plastic Telescoping Tubes are made of durable black plastic, tube is water-resistant. Features twist-off screw cap and removable, adjustable shoulder strap. Alvin is one of the primary sources for drafting supplies and drawing equipment in the country. Creative Coldsnow is a pround retailer of Alvin graphic arts, drafting and fine arts products.