With all of the different airsoft models out right now, there is a huge variation between different mechbox types. Knowing the differences, advantages and limititations between different mechboxes can be a determining factor when choosing AEGs. While mechanically they all do the same thing, they all have slight differences that make them unique.

Parts in a Mechbox

Spring - This determines your power. TM springs being the standard (almost all of which are about 280FPS-310FPS), most aftermarket springs are either based upon a percent of them (i.e., PDI 170 = 170% of original power, or 400FPS) or after-market springs are based upon the meters per second rating (i.e., M120 = 120 meters per second or 400FPS).

Cylinder - Comes in multiple types. The types are determined by the barrel length you are using. Using the correct type can affect FPS and efficiency.

Cylinder Head - Critical part to getting a good air seal. Determined by the mechbox version you have. Most are not interchangeable.

Nozzle - What directly pushes the BB into the hop-up unit. Determined by the gun that you are using, not the mechbox version, as all guns have different hop-up units.

Tappet Plate - The piece that makes the power transfer between gears and nozzle. Determined by the mechbox version you have.

Bushings - Hold the gears into the mechbox. These are almost the only universal part. The normal diameter for bushings is 6mm, but also come in 7mm, 8mm and even 9mm.

Gears - Transfers power from the motor to the piston. Ninety-nine percent of gearboxes use the three-gear system, including the Bevel, Sector and Spur gear. Gears are not universal between mechboxes and vary GREATLY for different purposes.

Piston - Fairly standard part. Comes either half-toothed or full-toothed. Full-toothed is by far the most common.

Piston Head - The main aspect to getting good compression in a airsoft gun. Comes in two versions, ported and non-ported.

Spring Guide The rod that will guide the spring and make sure no buckling occurs.

Anti-Reversal Latch - Used to make sure that gears do not wind backwards.

Motor - powers plant of the gun. Quality of the motor can have huge effects on rate of fire under different spring loads.