Specna Arms Set of Steel Shims

Specna Arms Set of Steel Shims is an adjustment set for AEG gearboxes that allows you to position the gears precisely. A correctly shimmed gearbox runs more smoothly, produces less mechanical resistance and extends the service life of the gears, bearings and the gearbox itself.

With virtually every gearbox upgrade or overhaul, shimming is a step that makes the difference between a replica that functions well and one that remains reliable in the long term. By setting the correct spacing between the bevel, spur and sector gears, you prevent excessive lateral load, unnecessary friction and premature wear. This is evident not only in a quieter gearbox, but also in a more consistent firing pattern and more efficient power transfer from the motor to the gears.

Why is it important to shim a gearbox correctly?

Many riders invest in faster gears, stronger springs or a more powerful motor, whilst the alignment of the gears remains unchanged. This creates additional resistance and wear and tear, meaning that new parts never reach their full potential.

A precisely positioned shim ensures that each gear runs at exactly the right height. This allows the teeth to mesh perfectly without exerting unnecessary pressure on the bushings or bearings. During a gearbox overhaul, it is immediately apparent how much smoother the entire drivetrain runs once the play has been correctly adjusted.

Performance during use

A well-shimmed gearbox does not result in a higher FPS, but it does make for a noticeably more efficient drivetrain. The motor has less resistance to overcome, which means the gearbox runs more smoothly and the internal components are subjected to less strain.

You’ll notice this, for example, when:

• whether you fit a high-speed or high-torque gearset;
• uses a high-capacity LiPo battery;
• fits a heavier M120 or M130 spring;
• Your replica is used intensively during skirmishes or long training days.

It is precisely with builds of this kind that the load on the gearbox increases, making correct shimming increasingly important.

Practical insights that are often underestimated

A common mistake is to allow each gear to rotate completely freely. Too much play means that the gears can still tilt under load, resulting in uneven stress on the gear teeth.

A second point to bear in mind is that new gears do not automatically require the same shim thickness as the original gears. Even CNC-machined gear sets can have slight tolerances, meaning that the existing shimming is no longer optimal.

It is also often forgotten that new bushings or bearings can affect the position of the gears. After every internal upgrade, it is advisable to check the entire gearbox again, rather than just the parts that have been replaced.

Material and dimensions

This Specna Arms shim set consists of steel shims in three different thicknesses. By combining several sizes, you can position the gears with great precision without any significant changes in height.

The set contains:

• 10 × 3 × 0.1 mm
• 10 × 3 × 0.3 mm
• 10 × 3 × 0.5 mm

Steel retains its dimensional stability under prolonged load, ensuring that the adjustment remains stable even after many gearbox cycles.

Compatibility and loadout

The shims are suitable for virtually all standard AEG gearboxes that use 3 mm gear shafts, including many Version 2 and Version 3 platforms.

They are often combined with:

• new AEG gears
• bushings or ball bearings
• a new piston
• a gearbox shell
• an AEG motor
• high-quality gear grease during assembly

By coordinating all the components simultaneously, the result is a powertrain that not only operates more efficiently but is also easier to tune.

Key features

• Three shim thicknesses enable highly precise alignment of spur, bevel and sector gears.
• Steel version retains its dimensions under prolonged mechanical stress and prevents rapid deformation.
• Reduces mechanical resistance, allowing the gears to turn more smoothly and reducing the load on the bearings.
• Suitable for maintenance and upgrades of most Version 2 and Version 3 AEG gearboxes with 3 mm gear shafts.

Who is this shim set suitable for?

This set is designed for players and airsoft technicians who are overhauling a gearbox, fitting new internal parts or looking to improve the reliability of their replica. Whenever a gearbox is fully disassembled, re-shimming is actually the correct procedure.

If you are using only a standard replica without any internal modifications and the gearbox is not opened, this set offers little benefit on its own. In that case, it is wiser to leave the existing settings as they are.

For high-speed builds, DMR projects and high-performance spring configurations, precise shimming is one of the most important steps in preventing malfunctions and premature wear.

What thicknesses are included in the Specna Arms Set of Steel Shims?
The set contains 30 steel shims: ten at 0.1 mm, ten at 0.3 mm and ten at 0.5 mm. This allows you to fine-tune virtually any gearbox.

Will this shim set fit in any AEG?
The shims are suitable for most AEG gearboxes with 3 mm gear shafts, including many Version 2 and Version 3 platforms.

Does shimming increase the FPS?
No. Correct shimming does not directly increase power, but it reduces internal resistance, allowing the gearbox to operate more efficiently, smoothly and reliably.

Do I need to re-shim the gearbox when fitting new gears?
Yes. New gears may differ slightly in size from the original set. It is therefore advisable to re-adjust the entire gearbox.

Can I combine these shims with other internal upgrades?
Certainly. They are often used in combination with new gears, bushings, bearings, pistons, motors and gearbox overhauls to optimise the entire drivetrain.

Do you want to build up the internal performance of your replica properly from the ground up? If so, the Specna Arms Set of Steel Shims is a sensible investment for a precisely tuned and durable AEG gearbox.