This is a tested model rocket similar to the OLD Estes Mosquito rocket kit. It accepts standard A - C rocket engines and has an 1/8" launch rod guide.I am making this for a local rocket party. The engine compartment is slightly oversized for tape to be wrapped around the engine to make the proper fit. Flies Great! Maybe too Great! Can use A - C engines HOWEVER, if you want the possibility of getting it back, only use A types engines! I tried a C6-3 engine first, it is probably halfway to the moon by now. : ) This rocket is VERY light and uses tumble recovery, (engine is ejected.) I printed it using Raft and Exterior support. Make it with bright color filament or paint it to help find it. Have Fun!