Mechbox types - This is going off the Tokyo Marui standard. There are many variations out there including ones from G&G, Systema and so on. However, Tokyo Marui is standard for almost 90% of airsoft manufacturers.

Version 1 - Only used in the TM Famas series. First mechbox made by TM in 1991. Only AEG to still come with an EG560 "red label" motor. The gearset included is actually a high rate of fire ratio gear set. While the mechbox is capable of taking high FPS, the motor and gears are not capable of running well over 400fps with .2g BBs. There is currently no replacement motor available. That being said, the Version 1 mechbox comes stock shooting 1000 rounds per minute using an 8.4volt battery, the highest of any stock AEG. Without tampering, this gun will run forever.

Version 2 - Used in MP5's, M16's, G3's and ect. This is by far the most used version mechbox and therefore has the most after-market help available. However, because of the design, this mechbox has trouble handling higher fps. The design lends itself to breaking of the front end if high fps is run for long times. Although reinforced versions of the V2, mechbox are available, many of them are reinforced in the wrong areas to do any good. While they are not the perfect mechanical series, there is so much after-market support available for this series, that they are a solid choice.

Version 3 - Used in series such as AKís, SIG, G36, and MP5K. This mechbox is a workhorse. Capable of running up to 600FPS without reinforcing, they are a far better choice for high FPS projects. Untouched Tokyo Marui Version 3 mechboxes have run in Iowa here for almost a 1/2 million rounds, which is more than the average player will do with a gun. These days there is almost as much after-market support of the Version 3 mechbox as the Version 2. If you like a series that is equipped with a Version 3, then this is the smartest choice for a long running AEG.

Version 4 - Only used in the TM PSG-1. Unlike all other versions, the Version 4 is a pre-cocking system, meaning as soon as you pull the trigger, it fires and then cycles the gun. The Version 4 is also a two-part mechbox; in fact, it is the original of this type. The top of the mechbox holding the cylinder, cylinder head, nozzle, tappet plate, piston, piston head, spring and spring guide can be detached from the bottom part housing the gears. This mechbox was designed specifically for semi-automatic fire only. This mechbox can also handle very high FPS.

Version 5 - Used in the TM UZI only. This is the only mechbox that has a plastic casing. This gun has an overly complicated design and with the lack of after-market support is extremely hard to work on. The mechbox is a very good performer, however upgrade potential is limited. Don't let the lack of after-market support turn you away from this gun.

Version 6 - Used in the Thompson and P90. This version is much like the Version 3. It is a tank and coming out with more and more after-market support.

Version 7 - Used only in the M14's. Different then all of the other guns listed so far, as itís built for torque. TM foresaw that this gun would more than likely be used for DMR (Designated Marksman Rifle) projects and built it that way. This mechbox is capable of 700FPS before needing a new shell. Almost all parts are unique for the Version 7, however many after-market parts are available.

Version 8 - Used only in the Type 89. It is a modified Version 2 mechbox with mechanical three round burst added. Many, if not all, of the Version 2 parts work in the Version 8.

Version 9 - Used in only the TM AKM74 and AKS74U. These were the first two guns to use the recoil engine designed by TM and have the correct angle for AK pistol grips. Almost all parts are unique, however more and more support is becoming available. This version is based off a modified Version 3 mechbox.

Version 10 - Based on a highly modified Version 2 mechbox. This is TM's new M4 mechbox with a recoil engine. As the gun is only a month old, after-market support is limited at the moment. This mechbox incorporates features such as cycle interruption that stops the gun when there are no more BBs in the standard mag.