ZCI produced 8mm gearbox shell for older ARES style receivers.  These gearboxes will generally fit into normal lower receivers.  They use a micro-switched trigger. 

*** You cannot fit any standard sized ETU (Perun Hybrid, Gate Titan etc).  Jefftron do an ETU which reportedly fits ****
*** Cannot fit 12:1 or 13:1 gears without modification to the shell ***

Features
- FRONT-WIRED
- 8mm (Does not include bushings or bearings)
- Tamiya connector
- Screws included
- QD spring guide included
- Selector plate included
- Cut-Off Lever included
- Safety Lever not needed