The Echo1 Version 2 Gearbox is a 7mm Gearbox for M4/M16/MP5 series airsoft rifles. This gearbox will fit most major brands from Tokyo Marui, JG, Echo1, AGM, G&G and more. This gearbox may require modification work to fit your airsoft gun.
The gearbox of my AGM M4 broke and i have to replace it with a new one. I found this echo 1 gearbox and thought i give it a try. This gearbox is a bit better quality than my AGM gearbox and better than the stock echo 1 gearbox that i saw a few years back. It is for a 7mm bushing and i have to purchase that. installed it and it functioned with out a hitch, i dont know why but my airsoft gun even shoots 30 fps stronger.. maybe it was the gear box or maybe everything was just placed percectly... that i dont know.. I am happy with my purchase and will recommend this to a friend.