Summary
This is a replacement body post for Traxxas models (and probably others) that uses a screw-on thumb cap instead of the body pins.  It requires a 30mm M3 screw that comes up through the bottom and goes all the way through the post for strength.  This works best when printed with TPU or other flexible filament.

This object was made in Tinkercad. Edit it online https://www.tinkercad.com/things/69ZEp6RPDT3

Print Settings
Printer brand:
Monoprice

Printer:
Maker Select

Rafts:
No
Supports:
Yes
Notes:
2mm walls recommended. Support required for post, not for cap.