The following information details the Estes body tube sizes. 

Nearly all matching Estes parts have the same series description # and are interchangeable. For instance, a body tube BT-20 will mate with a nose cone NC-20. A transition adapter TA-2060 will adapt a BT-20 to a BT-60. A 2050 centering ring will center a BT-20 in a BT-50.

	SIZE	INSIDE DIM. mm/in	OUTSIDE DIM mm/in	LENGTH cm/in
	BT-5	13.2/.518	13.8/.544	45.7/18.0
	BT-20	18.0/.710	18.7/.736	45.7/18.0
	BT-50	24.1/.950	24.8/.976	45.7/18.0
	BT-55	32.6/1.283	33.7/1.325	45.7/18.0
	BT-56	33.1/1.304	34.2/1.346	45.7/18.0
	BT-60	40.5/1.595	41.6/1.637	45.7/18.0
	BT-80	65.7/2.588	65.7/2.60	36.1/14.2

Body tubes are made of spiral wound paper. Use tube couplers to connect tubes of the same diameter. Use transition adapters to transition from one tube size to another.