Estes B4-4  Standard 18mm Rocket Engines (3-Pack)

 

Estes Standard 18mm Engine 3-Pack.  Standard Estes engines fit the standard BT-20 body tube and are 2.75" (7.0cm) long and 0.69" (18mm)  in diameter. 

3 pack includes engines, instructions, igniters, and igniter plugs.