It is intended to be attached with tape to a 6-8mm diameter wood stick. 

The advantage of this model is that it has a housing at the tip to add a smooth 8mm steel or aluminum rod  in diameter and also includes a cylinder to press the sugar. This is how the finished rocket, with the hole already made perfectly concentric and straight for a stable flight.

It was tested several times.

Parts list

• 3d printed Rocket itself
• 3d printed Print the pusher (this can be reused several times!)
• 120mm steel, aluminum rod. Plastic might work. make sure it is completely smooth
• 500mm straight 6-8mm diameter wood stick
• Sugar-potassium nitrate fuel