Motor Retainers BT-20 and BT-50 Estes compatible

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These motor retainers are designed to be interchangeable with Estes BT-20 and BT-50 motor retainers, so if you have lost a cap, you can just print a replacement and use that.  If you have an extra cap for some reason, you can print a base to pair with it.

The base glues onto the body tube and the cap screws on to keep the model rocket engine in place.

I included a taller version of the cap because I like to glue a thrust ring in the body tube so ¼ inch of the motor sticks out past the end of the base, making it easier to remove.  When you do that you need a longer cap.

The extra tall BT-50 cap allows you to use a E motor when the engine block was set for a D motor, rather than set the engine block for an E motor and using a spacer. The extra inch of the longer E motor will hang out the back instead.  Please be aware the doing this will shift the center of gravity back, so test for stability before using this in flight.

I would not recommend printing this with PLA due to the heat exposure.  PLA+ might work well enough, ABS for sure.  No supports are needed.  I printed with a .4 nozzle and .2 layer height with the Outer Wall Line Width to .3  For the BT-20 a .2 nozzle might give a smother result but isn't a must.

Thread specs:
BT-20: pitch 1.525mm, base diameter 22.25mm, cap diameter 23.5mm
BT-50: pitch 2.12mm,   base diameter 30.85mm, cap diameter 33.6mm

June 28, 2023 UPDATE:  reduced thread diameter setting on the BT-50 cap from 33.85 to 33.6 for a tighter fit so it won't skip threads if overtightened

June 29,2023 UPDATE:  Added extra tall cap, see warning above.