Estes package of seven assorted tube couplers. Couplers allow you to replace damaged body tubes with a section of new tubing, or for gluing body tubes together to create longer rockets. Couplers are also useful in cutting tubes. They're also an important part for building staged rockets. Two couplers for BT-55, BT-56, and BT-60 body tubes. One coupler for BT-80 body tube. Spiral wound cardboard: 1 brown, 4 red. Hints on using tube couplers to join two tubes together provided.