Am selling the engine only! While these engines get a lot of hate in the airsoft world it has ran extremely well for me however i ran across a polarstar so im running that now. This engine will only work in a standard v2 gearbox and is essential a polarstar clone as far as functionality goes. This would be best as a budget efficient way to get into hpa. For 150 bucks this engine will out preform an aeg gearboxes of two to three times the cost so if ur interested in getting into hpa give this a try -hpa consistently -Cheep -programable rps,fire mode dwel ect -adjustable fps play dmr or cqb with the same gun -already shimmed the trigger for fast semi auto play -wont kill the battery if left in the gun like other engines do!!!