The airsoft gearbox shell, or just gearbox shell, is a housing found in Airsoft Electric Guns, or AEGs. The gearbox shell serves as a special encasement for the main mechanisms at which electric airsoft guns generate compression that serves as the driving force to propel BBs.
Due to the many different shapes an airsoft replica may take, the gearbox shell may be designed a certain form factor to conform to those varied shapes. However, their function and overall operation design remains the same across all types. The differentiation of gearbox form factors are expressed in versions.
A difference in version may also carry advantages inherent of their design. For example, the version 3 gearbox found in AK and G36 variants have a more robust front end and can comfortably handle heavier main spring loads compared to most standard version 2 gearboxes like the ones shown in the images.
To overcome characteristic weaknesses, manufacturers may opt to apply improvements to standard gearboxes in the form of structural changes or the use of stronger materials.