A rocket needs to be able to accommodate motors of different lengths. Therefore a motor block in the motor mount tube is not used to keep the motor from moving up through the rocket. Most reloadable motors are manufactured with a lip on the aft (nozzle) closure as a thrust ring to prevent the motor from moving up through the rocket. However, motor and rocket kit manufacturers usually do not provide a means to keep the motor from falling out after burnout.
Several options are available. Some must be added during construction. Some can be added after a rocket has been finished.
A common practice is to install a #6 T-nut (also called a blind nut) into the aft centering ring. A hole is drilled into the ring for the barrel of the T-nut. The pointed anchors can be flatted because most centering rings are too thin to use them. A little epoxy around the edge of the T-nut will hold it in place. A screw can then be used to keep the motor in the motor mount tube.
The clip is held in place by a screw into the T-nut installed in the centering ring. A panel clip is used on screen doors, and can be found in hardware stores in the section with screen door repair parts. The slot in the clip is part of the clip.
T-nuts cannot be added to an already constructed rocket. However, expansion bolts and other devices available in any hardware store can be also be used to add positive motor retention to an assembled rocket. Some companies have screw-on retainers that can be added to existing rockets.
Submitted by: Dean A. Roth