Airsoft Gearboxes

If you're a realism enjoyer becoming HPA-curious, this will convert you! The Kythera SA Mechanical HPA Engine Conversion Kit from PolarStar Airsoft is a mechanical HPA conversion kit for M4/AR-15 and AR-9 AEGs, designed as a drop-in replacement for the cylinder group of the version 2 gearbox.

Being a mechanical system means you don't need a battery, don't need to avoid rain and get to enjoy the feel of a trigger system designed to simulate real steel single-stage triggers, complete with an authentic, tactile break and reset. This variant of the Kythera is locked to semi-automatic fire only, making it ideal for those who prefer a precise double-tap to a burst.

While you don't get the programmable trigger and electronic tuning options of the JACK™ or F2™ engines, the Kythera SA is ideal for milsim skirmishers looking for a leap in performance, DMR builders seeking the easy route to a reliable high FPS build or CQB specialists seeking a realistic yet incredibly snappy trigger. If you seek next-level performance and realism in equal measure, the PolarStar Kythera SA belongs in your build!

The GATE EON Complete V2 Gearbox with TITAN II Bluetooth® is a fully pre-built, high-end AEG gearbox designed for players who want elite performance without the hassle of tuning. Developed using cutting-edge airsoft technologies and tested with over one million rounds fired, this gearbox delivers exceptional reliability, lightning-fast trigger response, and consistent output straight out of the box.

Configured to produce approximately 350 FPS / 1.2 Joules when measured with 0.20g BBs and a 300mm inner barrel, this short-stroked setup is ideal for UK skirmish sites. The system is optimised for inner barrels between 250mm and 430mm, ensuring efficient air usage and stable performance across a wide range of replica builds.

At the heart of the system is the TITAN II Bluetooth® ETU, offering wireless connectivity straight out of the box. Using the free GATE Control Station (GCS) app, you can fine-tune trigger sensitivity, fire modes, diagnostics, and protection settings live from your smartphone or PC. Combined with premium EON CNC internals and a reinforced drivetrain, this gearbox provides top-tier performance with long-term durability and true plug-and-play installation.

To protect internal components and ensure longevity, the out-of-the-box rate of fire is capped at 25 RPS, striking the perfect balance between speed and reliability.

The GATE EON Complete V2 Gearbox with TITAN II Bluetooth® is a fully pre-built, high-end AEG gearbox designed for players who want elite performance without the hassle of tuning. Developed using cutting-edge airsoft technologies and tested with over one million rounds fired, this gearbox delivers exceptional reliability, lightning-fast trigger response, and consistent output straight out of the box.

Configured to produce approximately 350 FPS / 1.2 Joules when measured with 0.20g BBs and a 300mm inner barrel, this short-stroked setup is ideal for UK skirmish sites. The system is optimised for inner barrels between 250mm and 430mm, ensuring efficient air usage and stable performance across a wide range of replica builds.

At the heart of the system is the TITAN II Bluetooth® ETU, offering wireless connectivity straight out of the box. Using the free GATE Control Station (GCS) app, you can fine-tune trigger sensitivity, fire modes, diagnostics, and protection settings live from your smartphone or PC. Combined with premium EON CNC internals and a reinforced drivetrain, this gearbox provides top-tier performance with long-term durability and true plug-and-play installation.

To protect internal components and ensure longevity, the out-of-the-box rate of fire is capped at 25 RPS, striking the perfect balance between speed and reliability.

If you're building up your CYMA SR-25 for DMR duty, the CYMA CNC Gearbox Shell for CM.098 SR-25 AEG is an essential part for durability and long-term reliability! This version 2 long gearbox shell is CNC machined from 6061 aluminium, enhancing strength considerably compared to stock alloy gearbox shells. 

Designed as a replacement for the original V2 long gearbox present in the CM.098 series, this gearbox shell features 8mm bearing/bushing ports and is cut for a quick-change spring guide (not included). If you want your CM.098-based DMR to last a lifetime, the CYMA CNC Gearbox Shell for CM.098 SR-25 AEG is the key!

If you're planning the move over to HPA to take your build to the next level, the PolarStar Airsoft JACK™ HPA Engine Conversion Kit is a great way to do it! A drop in cylinder replacement single-solenoid HPA conversion kit, the JACK™ is available to fit either version 2 (M4/AR-15) or version 3 (AK-47/74) gearboxes, including everything you need other than your airline, regulator, air bottle and FCU battery.

Capable of a stunning 30 rounds per second in most setups, with more air volume and a wider range of velocity adjustment than its rivals, the JACK™ is highly efficient with a stunning response rate and a vast range of programmable customisation options built into the included fire control unit (FCU). If you're a performance seeker, the PolarStar Airsoft JACK™ HPA Engine Conversion Kit will change your game!

If you're planning the move over to HPA to take your build to the next level, the PolarStar Airsoft JACK™ HPA Engine Conversion Kit is a great way to do it! A drop in cylinder replacement single-solenoid HPA conversion kit, the JACK™ is available to fit either version 2 (M4/AR-15) or version 3 (AK-47/74) gearboxes, including everything you need other than your airline, regulator, air bottle and FCU battery.

Capable of a stunning 30 rounds per second in most setups, with more air volume and a wider range of velocity adjustment than its rivals, the JACK™ is highly efficient with a stunning response rate and a vast range of programmable customisation options built into the included fire control unit (FCU). If you're a performance seeker, the PolarStar Airsoft JACK™ HPA Engine Conversion Kit will change your game!

If you're after HPA performance with professional-level tuning options, the PolarStar Airsoft F2™ HPA Engine Conversion Kit is the way to go! An updated version of PolarStar's incredible Fusion™ engine, the F2™ is a dual-solenoid engine, allowing tuning of both the loading speed and air volume via the included digital FCU (fire control unit).

The set is designed to drop into either a V2 (M4/AR-15) or V3 (AK-47/74) gearbox (depending on the variant you choose), including everything you need other than your airline, regulator, air bottle and FCU battery.

Offering a variable rate of fire up to a stunning 30 rounds per second, adjustable velocity and a vast range of programmable options, including alternative fire modes, anti-stiction mode, "closed bolt" mode and "AEG" mode, the F2™ engine is the right choice for experienced HPA users looking to move up to a more complex, high-performance engine. If this sounds like you, the F2™ HPA Engine Conversion Kit belongs in your build!

If you're after HPA performance with professional-level tuning options, the PolarStar Airsoft F2™ HPA Engine Conversion Kit is the way to go! An updated version of PolarStar's incredible Fusion™ engine, the F2™ is a dual-solenoid engine, allowing tuning of both the loading speed and air volume via the included digital FCU (fire control unit).

The set is designed to drop into either a V2 (M4/AR-15) or V3 (AK-47/74) gearbox (depending on the variant you choose), including everything you need other than your airline, regulator, air bottle and FCU battery.

Offering a variable rate of fire up to a stunning 30 rounds per second, adjustable velocity and a vast range of programmable options, including alternative fire modes, anti-stiction mode, "closed bolt" mode and "AEG" mode, the F2™ engine is the right choice for experienced HPA users looking to move up to a more complex, high-performance engine. If this sounds like you, the F2™ HPA Engine Conversion Kit belongs in your build!

If you're looking for the cheapest and easiest way to convert your M4/AR-15 AEG to HPA, you just found it! The Ares Drop-in HPA Engine Conversion Set for M4/AR-15 V2 Gearbox is a complete set with a V2 gearbox shell, HPA engine and EFCS module all pre-built, saving you hassle sourcing the right parts while saving you a few quid as a bonus!

This HPA Engine Gearbox is designed as a drop-in replacement for standard M4/AR-15 AEG Version 2 gearboxes but it may need alignment and tuning to fit certain receivers and HOP-up units. To power the pre-installed EFCS, an 11.1V LiPo battery with an XT30 battery connector is required and the air line fitting is US spec, meaning it will only accept US-type air lines and won't work with EU-type lines. For those as yet uninitiated future HPA players; this set does not include an air line, regulator or air bottle and you will need these to get into the HPA game!

This is the semi/full auto version designed for non-ambidextrous M4/AR-15 AEG receivers and is equipped with a standard M4/AR-15 curved trigger, ideal for almost any build style. As with any internal upgrade, this engine will require expertise to install and some level of familiarity with M4/AR-15 AEG internals. If you're struggling, you can contact us or your local Airsoft tech for advice.

The Spenca CORE™ V2 Gearbox Shell provides 8mm bushings, radiused cylinder windows to help prevent cracks, and quick release spring functionality. Perfect for starting your ultimate gearbox build!

If you've decided to join the dark side and HPA your M4, this set will sort you out! The Storm Airsoft HP-R Storm System HPA Engine is a complete drop-in conversion kit for rear-wired version 2 gearboxes, packaged with everything you need to convert your AEG, bar the usual HPA regulator, airline and hose.

The included FCU offers a wide range of adjustable parameters, including programmable fire modes, rate of fire adjustment, and nozzle dwell time adjustment, ensuring reliable feeding with every shot. While it is a drop-in kit, this set will require a certain amount of familiarity with AEG internals and HPA. Luckily, Storm Airsoft provides a useful installation video which makes the process even easier.

Benefits of running HPA over a standard AEG gearbox include minimal FPS deviation between shots for improved accuracy, near-instantaneous trigger response for cranking out those double taps and a wide range of tuning options and adjustments, perfect for casual skirmishers looking to take their build to the next level. If you want the competitive edge HPA provides with minimal effort, the Storm Airsoft HP-R Storm System HPA Engine is the way to go!

A pre-assembled, ready to use complete gearbox set designed for use in 6mm Airsoft BB replica M14 AEGs. With all the components assembled and in place, this gearbox is ready to be dropped into place in your M14 AEG, replacing any old and worn out gearboxes.

If you find your springs are wearing down faster than they should you need a replacement spring set!

This  pack comes with 6 different types of spring including:

• Switch Return Spring
• Tappet Plate Spring
• Anti-Reversal Lath Spring
• Stopper Arm Spring
• Selector Plates spring for Version II
• Trigger Return Spring

The springs are designed for use with version 2 gearboxes, for AEG rifles such as M4s, AR36s, SMG-5 and more!

If you love working on gearboxes or have a version 3 custom build on the cards, the FPS Softair Complete Gearbox Spring Set for V3 Gearbox belongs in your toolbox. This set includes all of the springs needed for a version 3 gearbox build, including the tappet plate spring, ARL spring, motor height spring, cut-off lever spring, trigger return spring and switch return spring.

All of the springs in this set have been manufactured by FPS Softair to be more durable than the original springs and with more precisely calculated tension for maximum efficiency. Whether you've lost a spring, are working on a version 3 gearbox build or need spares for your technical projects, the FPS Softair Complete Gearbox Spring Set for V3 Gearbox will be useful addition to your parts bin!

A shell for gearbox type V2 with reinforced aluminium construction. The front part has been strengthened with the most exposed area being considerably thickened and the area of the contact with the cylinder has been improved so as to evenly transfer the loads.

The shell is mounted using its 8mm bearings. This gearbox shell is designed for use in J.G replicas but should potentially work in replicas of other makes and manufacturers.

A complete V6 gearbox designed as a replacement for CYMA P90 AEGs to breathe new life into your weapon.

If you're done with AEGs and want to revamp your build for HPA, the GATE PULSAR D Dual Solenoid HPA Engine is a fantastic option. Designed for Version 2 AEG gearboxes, the PULSAR D is designed to work with a GATE TITAN™ II V2 ETU (HPA Version), giving you unlimited advanced programming options along with the bob on consistency, top-tier accuracy, killer rate of fire and wealth of tuning opportunities HPA builds are known to provide.

The set includes the complete engine but will require a V2 gearbox shell, V2 trigger and TITAN™ II ETU HPA Version to complete the build. When compared to the original and more affordable PULSAR S, the PULSAR D offers a higher FPS range, universal compatibility with AEG nozzles, less precision required in the assembly of the build and impressively high air efficiency, using only 0.7 PSI per shot on average at 90 PSI with a 0.8L air tank.

The PULSAR D also has the edge in accuracy and versatility over the simpler single solenoid PULSAR S, being suitable for any build objective, from CQB monster to DMR dominator. As with all internal upgrades, we only recommend this engine to those who are confident working on AEG and HPA internals, but if you're ready for the PULSAR D, you're sure to be impressed!

Specna's ORION™ reinforced gearbox has gained an excellent reputation since it was released installed in the EDGE™ series of AEGs, and now Specna are offering you the opportunity to create your next gearbox build with a solid, reliable shell to tie it all together. Rated to handle heavy springs and including enhancements such as radiused cylinder windows and quick change spring functionality, the ORION™ gearbox shell is probably a tad more affordable than it should be!

If you've encountered issues with your Specna Arms PRIME™ M4/AR-15 AEG's gearbox, you're in luck! This replacement gearbox shell is an original replacement part, allowing you to revive your AEG back to good health. It comes with the J-Cage bearings pre-installed, meaning it is unlikely to be compatible with other AEGS.

This reinforced Gearbox has an anti-reversal release window, pre-cocking and AoE inspection windows, reinforcements in high-stress areas, a motor gear inspection window, a trigger adjustment function and screw holes allowing for easy alignment. Get a quick fix for your PRIME™ AEG with the Specna Arms Aether™ V2 Gearbox Shell w/ J-Cage Bearings!

Ideal for reviving worn out RIFs or as a backup for a rainy day, this is a complete and assembled gearbox including motor, that is ready to drop into any compatible Version 2 accepting replica.

Building a gearbox from scratch? You'll need a shell to get started! The ARCTURUS Version 3 Alloy Gearbox Shell is a reinforced design with a radiused cylinder window, additional material surrounding the cylinder for extra strength and 8mm bearing holes. The rear of the gearbox is also cut for a quick change spring guide.

The version 3 shell is common to AK, AUG, AR36 and SMG-5K AEGs (not the regular SMG-5, though) so if you need a gearbox shell for any of these platforms this one will be compatible in most cases.

If you're working on a high-speed or high FPS build, the Delta Armory Version 2 CNC 8mm QSC Gearbox Shell will save you a lot of heartache in the long run! This ultra-strong version 2 gearbox shell is CNC machined from the best aluminium around, known as 7075 T651. This means if you're running a super strong spring or going for a dual-sector gear build, this gearbox shell has what it takes to keep running in the long term, being considerably stronger than standard alloy gearbox shells.

The QSC Gearbox shell also features radiused cylinder window corners to better distribute force and is pre-cut for Gate TITAN/ASTER, Perun Hybrid or Delta Armory ETU MOSFET systems, meaning no need to get the Dremel out to add advanced functionality. The bearing ports are 8mm in diameter, making this the perfect host for Bolster Armouries EZO Ball Bearing Bushings. If you're reaching for the stars when it comes to performance and want your build to last more than a few bursts, the Delta Armory Version 2 CNC 8mm QSC Gearbox Shell is what you need!

If you are building a version 3 AR36 gearbox or you have an old AR36 AEG that needs a refit, this spring set will be useful! The set includes all the springs needed to complete a version 3 gearbox for AR36 AEGs except for the mainspring (the spring that provides the power). Maybe you have lost a spring, or your tappet spring got chewed up after a long and hard life? This spring set should give you all you need to get your AR36 doing its dirty work once again!

If you are looking for a high end gearbox shell to start your ultimate AEG build, stop looking, you found the best there is! The Gate EON gearbox shell is CNC machined from 7075 aluminium for a strong and lightweight gearbox with a plethora of small enhancements that make this gearbox a dream to put together.

The cylinder window is radiused on all corners and the shell has some significant reinforcements at the front end, and along the top spine. The internal wire routing has been redesigned for ease of installation, and the shell is perforated with several inspection windows so you can set your angle of engagement, adjust your pre-cocking settings and shim your gears perfectly. Is this the ultimate Airsoft gearbox? Well, it will be, once you've built it!

If you are looking for a high end gearbox shell to start your ultimate AEG build, stop looking, you found the best there is! The Gate EON gearbox shell is CNC machined from 7075 aluminium for a strong and lightweight gearbox with a plethora of small enhancements that make this gearbox a dream to put together.

The cylinder window is radiused on all corners and the shell has some significant reinforcements at the front end, and along the top spine. The internal wire routing has been redesigned for ease of installation, and the shell is perforated with several inspection windows so you can set your angle of engagement, adjust your pre-cocking settings and shim your gears perfectly. Is this the ultimate Airsoft gearbox? Well, it will be, once you've built it!

Redesigned for maximum compatibility with a wide variety of brands, the RetroArms CNC QSC Gearbox V2 is ideal for technical Airsofters working on a high-performance build which needs to last a lifetime. The set includes a Version 2 gearbox shell, carbon steel screws and a steel ball bearing spring guide and is ideally used for extremely high ROF or FPS builds. 

The shell itself is precision machined using CNC technology from the best aluminium around; 7075 T651, an ultra-hard alloy with similar strength properties to steel, boasting an ultimate tensile strength of 590 MPa compared to construction steel's 390 MPa. The quality of the machining simply cannot be overstated; every surface is flawlessly smooth and finished to perfection. 

Not content with making an absolutely beautiful gearbox from the finest materials around, the team at RetroArms has also put a lot of thought into the design aspect, improving on the original Tokyo Marui V2 gearbox in several areas. The piston tracks and selector plate rails have been redesigned for wider compatibility, the front of the gearbox is enlarged in every dimension to improve strength, "glue pockets" have been added around each bearing hole so they can be glued in and wider internal wiring routes for heavy gauge wiring, along with much, much more. If you're the techy type seeking a slick gearbox shell to start your build, the RetroArms CNC QSC Gearbox V2 is exactly that!

This SR25 Gearbox set by CYMA is designed to fit right into most SR25 / AR25 / AR10 style Airsoft Rifles / Guns. Included is a Piston, Cylinder, Gear Set, Tappet Plate, Nozzle. This GEARBOX set does not come with the shell, internals only.

Whether you're building an AK from scratch or you need a refurb, the Specna Arms Reinforced V3 Gearbox Shell w/ Micro-Contact is ideal. Made from alloy and finished in metallic blue, this V3 gearbox shell is pre-fitted with an AK trigger, micro-switch trigger contacts, a mini-Tamiya connector and all the necessary wiring. 

Compatibility-wise, this is designed for most AK AEGs, but the shell alone can also be used in other V3 gearbox-compatible AEGs (AUG, SG55x, & AR36), provided you remove the trigger and other AK-specific parts. The set also includes a quick-change spring guide, allowing you to tune power easily without opening the gearbox itself. 

The bushing ports are 8mm in diameter, so when choosing bearings/bushings, go for 8mm examples. If you need a cheap replacement gearbox shell for a refurb or scratch build, the Specna Arms Reinforced V3 Gearbox Shell w/ Micro-Contact is a fine choice!

If you are building a version 3 AK gearbox or you have an old AK AEG that needs a refit, this spring set will be useful! The set includes all the springs needed to complete a version 3 gearbox for AK AEGs except for the mainspring (the spring that provides the power). Maybe you have lost a spring, or your tappet spring got chewed up after a long and hard life? This spring set should give you all you need to get your AK doing its dirty work once again!

If you have an old ICS L85 or L86 that needs fixing up, this is a great part to pick up! The ICS L85/L86 Gearbox Shell is an original replacement part for those platforms. It is constructed from alloy and comes with steel screws for securing. It's a unique shape and is unlikely to fit any other Airsoft replicas.

This is a great item to pick up if your current gearbox is cracked or you fancy experimenting with what upgrades can actually fit inside an ICS L85/L86.