Internal Upgrades
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Internal parts refer to various gearbox, inner barrel, and hop up components. Whether it is a repair that you are working on or you are looking at increasing the fps, rof, or durability of your airsoft gun, Zephyr Sports has you covered.
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Raptors Airsoft RTX Maple Leaf Gas Hop Up Bucking - 70 Degrees
Zephyr Low Price: $9.95
Save: $2.00 (16%)
Mad Bull M130 Airsoft Upgrade Spring
Zephyr Low Price: $16.95
Save: $3.04 (15%)
Mad Bull M110 Airsoft Upgrade Spring
Zephyr Low Price: $15.95
Save: $4.04 (20%)
Modify Airsoft 7mm Steel Bearing Bushings - Set of 6
Zephyr Low Price: $24.95
Save: $5.05 (16%)
Mad Bull Airsoft Polycarbonate 1/2 Tooth Piston Body
Zephyr Low Price: $22.95
Save: $3.05 (11%)
Modify M120 Airsoft Upgrade Spring
Zephyr Low Price: $14.95
Save: $2.04 (12%)
Echo1 M16 Complete Gear Box with MOSFET
Zephyr Low Price: $149.95
Save: $20.00 (11%)
King Arms Ver. 3 8mm Bearing Gearbox w/ AK Selector Plate
Zephyr Low Price: $64.95
Save: $15.00 (18%)
Bravo Airsoft Aluminum Cylinder Head for Version 3 Gearbox
Zephyr Low Price: $19.95
Save: $2.05 (9%)
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More Information:

Bearings and Bushings

Airsoft AEGs use 6 different bearings or bushing in the gearbox shell that connect with the gear's axles and allow the gears to spin freely. Bushings are solid pieces of metal, that can take a greater amount of stress and pressure than bearings. Bearings use ball bearings to rotate with the axle and create less friction but they can break. AEGs can use between 5mm and 9mm bearings and bushings with 6mm arisoft bushings being the most common type.

AEG Cylinder Sets

This section includes all airsoft cylinders, cylinder heads, and air nozzles that we carry. Air nozzles and cylinder heads are often proprietary and will require a specific combination to function correctly. Cylinders however are universal and are interchangeable between 90% of AEGs. Cylinders have a variety of cuts (O or none, 3/4 and 1/2) that correspond to the AEG's barrel length to maintain a volumetric ratio. The cylinder head caps the end of the cylinder while holding it in place in the airsoft gearbox. An air nozzle is designed to work with the tappet plate to load BBs and transfer air from the cylinder into the hop up and barrel.

Gear Sets

Gears are one of the most important parts of an airsoft AEG and largely determine the power of the spring the gearbox can cycle. Sector, Spur, Bevel and Pinion airsoft gears can all be found here in various ratios depending on the player's need. The Pinion gear is attached to the motor and drives the bevel gear that changes the direction of the motor's spin force. The spur gear acts to change the torque power in the gear system and the sector gear pulls back and then releases the piston to fire the AEG.


AEG and some sniper barrels are in this category. Airsoft AEG barrels come in a large variety of lengths and bores to increase the accuracy of airsoft guns. An increase in length will always out do a decrease in bore size to improve accuracy. Additionally, some smaller airsoft barrels will require much more power from an AEG spring in order to gain higher fps values since more air is wasted.


Airsoft motors usually come in three different varieties. Torque motors provide the greatest turning force but sacrifice speed for power. Speed motors are able to achieve high rotations per minute, but are unable to provide as much power. Standard motors are the compromise between speed and power and often are found in stock airsoft guns.

AEG Pistions

The piston attaches to the piston head and is driven forward by the spring along a pair of guide rails built into the gearbox shell. Pistons typically have some number of metal teeth to take the strain off of the piston body and keep the teeth from stripping out. There are two types of pistons, half tooth and full tooth pistons. Full tooth pistons can be used with most AEGs and gear sets, they are the most common of the two types. A half tooth airsoft piston is made to work with Sector gears that have teeth that extend out near the half moon teeth. It is not recommended that you use a half tooth with a regular sector gear, and a full tooth piston can break a gearbox if used with a long tooth sector gear.

Gear Boxes

Some times, not getting into the gearbox is easiest. This section houses AEG shells, and full drop in gearboxes that are ready to go out of the box. Echo1 has released a fully upgraded V2 gearbox drop in that features a Mosfet unit.

Spring Guides

Most spring guides are made of plastic and feature a washer to prevent the spring from wearing them down. A metal spring guide is far superior because it guides the spring and piston without play and they include bearings. The bearing sits at the end of the spring guide and twists with the spring to reduce the stress the tension of the spring causes. Spring guides are pretty universal, a different model with each version of gearbox.


The AEG spring is the part of a gearbox that determines what fps the AEG will fire at. The harder the spring, the higher the fps, but in order to use higher power springs, AEGs must use higher torque builds to compensate for the increased power. Softer or lower power springs are often used in high rof builds to reduce the strain on the gearbox and allow the AEG to achieve higher rates of fire easier.

AEG Electronics

Upgrading an airsoft gun's wiring harness can improve the battery life, rate of fire, and trigger response of the airsoft gun. Mosfets can also be installed to create almost instantaneous trigger response and increase the efficiency of the airsoft gun. Mosfets can also reduce the stress and carbonization caused by using Lipo batteries.

Hop Up Accessories

Hop ups when tuned correctly can add lots of range to airsoft guns. By creating a backspin on the airsoft BB, the rotational inertia fights against the Earth's gravitational pull and can increase the range dramatically. A good hop up (typically metal) can also increase accuracy. The hop up bucking creates the seal between the barrel and the hop up, as well as imparting the spin onto the BB, and keeping the BB in the hop up until fired. A softer bucking will improve the spin imparted by a hop up and create a better seal. A harder hop up however, will last longer than its soft counterpart.

Miscellaneous Upgrades

From tappet plates to shims, all miscellaneous parts go here.