Mech Boxes
Tokyo Marui invented the first AEG with lots of R&D. Since then, other companies have ripped off the design. Marui was not clever enough to get proper patents first, but was still smart enough to make the world's best AEG - to this day. The first of these was the FAMAS. It had what is now known as the Version 1 mechbox. The mechbox is the metal shell that houses most of the internal parts of an Airsoft gun. The only true internal parts that are not located inside the mechbox are usually the inner barrel, the hop-up assembly, wiring, fuses, and the motor system. The metal shell and the internal parts combined are what is known as the mechbox. The mechbox is usually located in what is known as the receiver of the gun.

There are a total of 8 different mechbox “versions” that commonly exist on the market today that were innovated by Tokyo Marui. Any one version is not necessarily better than any other version, with the exception of some slight improvements with each subsequent version. The only major difference between the versions is the shape the mechbox shells are in and the arrangement of the internal parts. This is due to the shape of the different styles of guns that the mechboxes fit into. Otherwise the internal parts are pretty common across the board, with some exceptions. Here is a list of all the different mechbox versions that Tokyo Marui makes and the guns that they inhabit:

1) Version 1: FAMAS and FAMAS SV
2) Version 2: all M16 or M4 family of guns, MP5s, and G3s - the most common mechbox version
3) Version 3: All the AK’s, Sig 552, 550, 551, G36C, Mp5k, PDW, AUG
4) Version 4: PSG 1
5) Version 5: UZI
6) Version 6: Thompson and P90s
7) Version 7: all M14s
8) Version 8: Type 89

There are other mechbox types and versions made by other companies with their own numbering systems. However, the third party companies that make only parts and not guns, make parts only for Tokyo Marui and their numbering system. This chart works with companies that make direct clones of maruis such as classic army and some ICS. Some Classic Army, Echo-1 mechboxes are compatible with the above design, but not always. We will be posting new information as to what-fits-what, once we confirm the parts do match up. For instance, the Classic Army CA-25 gun, uses a Marui PSG-1 style upgrade spring. The bushings however, use their own proprietary size..