Includes 6 Tube Couplers in 3 different sizes. BT5, BT20 and BT50. Perfect for connecting 2 body tubes of the same size together! Technical Specifications 6 Tube Couplers 2 each. BT5. 1 inch long. 2 each. BT20. .75 inches long. 2 each. BT50. 1 inch long. Estes model rocketry is recommended for ages 10 and up with adult supervision for those under 12. Unless otherwise specified, all models require assembly. Tools, construction and finishing supplies sold separately. In order to launch, a launch system, model rocket engines, starters and recovery wadding are required - sold separately-unless otherwise specified.