Estes D and E Engine Mount Kit - Includes enough parts to mount two engines (3159)Heavy duty engine mounts for the D and E engines Contains enough parts to mount two engines Contains all the component parts for mounting one or two 24 mm D and E engines in BT 55, 60 and 80 body tubes. Includes 19 individual parts: 30052 Large Diameter Laser Cut Centering Ring (qty. 1) This BT 80 body tube centering ring set is laser cut from heavy duty cardstock and allows the model rocket builder the option to insert a single 4 in., BT 50 motor