Estes BT-20 Body Tube Pack - Includes 4 Tubes that fit NC-20 Nose Cones (3085)Four BT 20 body tubes per package. Use with NC 20 nose cones (sold separately). Strong and lightweight plain brown tubes with a thin wax coating Used for custom model rockets or repair work Can be cut to needed length. Use tube couplers to join tubes of the same diameter, or use as support while cutting. Inside Dimension 0. 710 in (18. 0 mm) Outside Dimension 0. 736 in (18. 7 mm) Length 18. 0 in (45. 7 cm)