An interesting comparison of Version 3 gearboxes from Retro Arms and X High Tech/Combat Gear is made by Hokum of Airsoft Ukraine... "From the technical point of view the ultimate difference between these two is in the process how they were made. The X High-tech gearbox is casted first and then milled (or if you prefer - polished with CNC). The one from Retro Arms is completely CNC machined out of the solid block of aluminium AW EN7075 T651.