The Modify-Tech V3 Torus Gearbox By Dom.
From: http://popularairsoft.com/reviews/modify-tech-v3-torus-gearbox/

Popular Airsoft wrote a Modify-Tech V3 Torus Gearbox Review for Modify-Tech. Dom try our V3 gearbox, and clearly described V3 gearbox's features. In the process of test, Dom raised an issue with Modify-Tech.

Modify-Tech with modifications based on a test review, the Modify Ver. 3 Torus gearbox now works well with the Marui AK and LCT AK AMD-65 AEGs.

Visit Popular Airsoft to check out the issue and read full review:  http://popularairsoft.com/reviews/modify-tech-v3-torus-gearbox