Bondtech Upgrade Kit for Prusa i3 MK3S & MK2.5S Mosquito Fit





Upgrade Kits


Prusa I3 MK3S Mosquito

EAN13: 7350011410675 SKU: EXT-KIT-69 Categories: , , , , Brand:

Prusa i3 MK3S+/MK3S / MK2.5S Mosquito IDGA

(2 customer reviews)

New Version WITH IDGA Shipping Now!

with new white plastic main gear and integrated drive gear for lower run-out

A lightweight high-resolution extruder upgrade for the popular Prusa i3 MK3S and MK2.5S 3D printers with optimized design to use Mosquito and Mosquito Magnum hotends.

Product Main Features

This extruder upgrade kit is for the Prusa i3 MK2.5S / MK3S / MK3S+.
These are its main features:

  • Adapted to fit Prusa’s new filament sensor and Mosquito hotends;
  • Includes one Bondtech BMG extruder drive train with 3:1 gearing ratio;
  • Optimized geometry for heat-sink cooling;
  • Mount for PINDA probe included;
  • Less moving weight to reduce vibration and ghosting;
  • Professional SLS 3D printed housing and 3 other key parts.



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This Upgrade Kit does not include the Bondtech drive gears. They are included in your Prusa already.

To use this Upgrade Kit, you will also need to buy the following:

Optional items:

Upgrade Your Prusa

Upgrade your Prusa with a Bondtech Mini Geared extruder featuring higher gear ratio – 3:1 – that allows for extra push force and higher resolution.

Print Faster Or With Higher Quality

This lightweight extruder will allow your 3D printer to print faster or to achieve even better surface quality.

Reduce 3D Printing Issues

Decrease the risk of heat creep to avoid clogs and improve filament feeding by avoiding slipping and deformation that cause under and over extrusion issues.

Upgrade kit With Optimized Design to fit Mosquito hotends

This is a Bondtech upgrade for the popular Prusa I3 MK3S+/MK3S and MK2.5S that will allow the use of the world acclaimed Mosquito hotends.

Bondtech Extruder For Prusa i3 MK2.5S & MK3S + MK3S+

This kit contains only the necessary parts to convert your current extruder to our own popular design based upon our BMG (Bondtech Mini Geared) extruder with 3:1 gearing ratio for better precision and resolution together with optimized geometry for the heatsink cooling and professional SLS 3D printed housing.

Working Temperature Limits

Bear in mind that if you use this upgrade kit inside a closed chamber, it will have the following set of working temperature limits:

  • Due to the sensor plastic parts made of HT PLA > up to 60°C (90-100°C when parts are annealed);
  • Due to the stepper motor > up to 80°C.

MK3S / MK3S Mosquito, What’s the difference?

This Upgrade Kit is mostly similar to the previous MK3S, with the main difference of having been designed to fit the Mosquito and Mosquito Magnum hotends.
Other differences come from the design changes that include:

  • An optimization of the cooling air channel to focus the airflow on the Mosquito’s heatsink. The channel is narrower.
  • This tighter space is also used to hold the hotend in place during nozzle changes, so the user can change the nozzle with a single hand.
  • The fan shroud was also redesigned to fit the Mosquito hotends.
  • We include in this kit a new part, the Mosquito hotend adapter, 3D printed with SLS.
Prusa’s Heater or Mosquito Heater, What should I use?

The Upgrade is compatible with the thermistor and 40w heater already supplied with the Prusa (MK3s).
A 30W heater(most mk2.5s users) will likely not be sufficient enough to keep the Mosquito Hotend at a stable temperature.
However, you also have the option of using Slice Engineering Mosquito thermistor and 50W heater.
We recommend the more efficient 50W heater for your Mosquito to reach a stable operating temperature faster.

  • If you have a Prusa i3 MK2.5S, buy the 12v Mosquito heater.
  • If you have a Prusa i3 MK3S, you should buy the 24v Mosquito heater.

We highly recommend using a thermal compound paste to provide good thermal conductivity between the heater and the hotend.
Slice Engineering recommend the use of Boron Nitride Paste.

Updating the Firmware

To use this upgrade in the MK2.5S / MK3S, the E-steps and Z_Max needs to be updated. Check out the latest version of our firmware here.
We are also supplying firmware versions compatible with the use of Mosquito’s thermistor.
If you are using this Mosquito’s component you should use the related firmware.


To use the MMU2s together with the Bondtech an extra Add-On is required. This will allow sensor to trigger once the filament is reaching the drive gears.
You can download the STL file bundles from our MMU2S Add-On Files tab.
All credits to Leon Van Roosmalen for his amazing design. Find more information about his work and designs here:

Community involvement

This is a co-development work with awesome guys in the Prusa Community like Chris Warkocki, Grégorie Saunier (Bear Upgrades), Olof Ogland, Erik Bjorgan, Josh Jones, Kyle Wiehe, Marc Evertz, Matt Harrison, Ocie Ward, Sando Bendig, Vecko Kojchevski (Vecko Extruder), Steven Mölby, and Yuri Delia that have provided excellent feedback and suggestions of how to develop the “perfect” extruder setup for the Prusa series printer. A lot of work has been put in this project and we tried to listen to all the inputs in order to find a solution that can be the best fit to the Prusa I3 MK3S.

Freight Weight 407 g
Dimensions 15.5 × 11.5 × 10.5 cm

Technical Specification

  • Article number : EXT-KIT-69
  • EAN code : 7350011410675
  • Net weight : 378g
  • Gross weight : 389g
  • Package Size : 137x94x65mm
  • Gearing ratio : 3:1
  • E-steps value : 415 @16 bit micro-stepping; or 830 @32 bit micro-stepping
  • Extruder Housing : SLS Printed parts in Polyamide 12;
Stepper Motor

Lightweight 25 mm pancake stepper with 18 N/m torque.
Max Input Current : 0.8A
Max chamber working temperature : 80℃

X-Carriage: Requires buying or 3D printing new X-Carriage R2 Front and Rear;
Firmware: Bondtech adapted version required.

Licensing: This Project is licenced under GPL V3.0 and the STEP-files are available for download.


Bondtech Github contains the STEP file, installation manual, exploded view, and more.

The STL Files For Additional Parts Required Available As Free Download

The 3D printed parts of this kit can be downloaded from our server.

MK2.5S: Click here to download the Front.
MK3S :Click here to download the Front.

MK2.5S / MK3S:  Click here to download the Rear.

Latest Firmware

Based on 3.13.3 Firmware for MK3, MK3S, MK3S+, MK2.5 and MK2.5S

The firmware archives you will find below are based on the Prusa release mentioned above. All updates were done by Bondtech to optimize the usage of our BMG based hardware and sometimes to tweak specific features. You may find more information on the release notes below.

MMU2S & MMU3 Support

This firmware release supports Bondtech customers that are using the MMU2S or MMU3 with Prusa i3 MK25s or MK3s, and E3D or Mosquito hotends. Expand the tab that fits your 3D printer and choose the firmware file most adjusted to your configuration.

About this release

Please read Prusa’s release note to know about all changes : 3.13.3 Firmware

Source Code

Click the link below to visit the Source Code page to clone or download.

Select the Bondtech MK3 FW3133 branch

The HT firmware versions should only be used with Slice's 450C thermistors.
For Slice's 300C thermistor, choose the non HT version.

Do not use any of the files below with LGX based Upgrade Kits.
For LGX based upgrade kits look for firmware on the related Product Page.

For RAMBo 10a Mainboards

For RAMBo 13a Mainboards

For RAMBo 10a Mainboards

For RAMBo 13a Mainboards

For RAMBo 10a Mainboards

For RAMBo 13a Mainboards

For RAMBo 10a Mainboards

For RAMBo 13a Mainboards

For older versions Click here

To learn how to install a firmware update on your Prusa i3

Click here

2 reviews for Prusa i3 MK3S+/MK3S / MK2.5S Mosquito IDGA

  1. Matthew Ostman (verified owner)

    One star above zero because, largely, it works as expected. Runs smoothly, bondtech performance you’d expect.

    The rest? Hope and pray you never have a clog, a jam, any sort of issue that requires you to access the hotend. Because, for reasons I struggle to imagine, this extruder is designed such that the screws that hold it together are also the screws that attach it to the x-carriage – and are subsequently buried WITHIN the x-carriage during assembly. There is zero affordance for any sort of maintenance access – if you need to get at ANYTHING it’s going to be a full teardown.

    • Joel Lennartsson

      Hello Matthew,

      Thank you for your feedback!
      You should however, be able to open the extruder for maintenance without tearing everything down.

      There are four screws clamping the extruder together.
      • 3x Screws from the back that you can loosen without removing the X-carriage cover (rear).
      • 1x Screw on the bottom front. Remove the part cooling fan to access.

      You then need to remove the right two screws holding the 4010 fan and unplug the motor cable.

      Now you can split the housing parts and let the rear housing rest on the screws.

  2. Herschel Boyd (verified owner)

    Fantastic upgrade to the already rock solid Prusa Mk3S. Will be upgrading the rest of my fleet with the Mosquito Magnum. Everything you would expect from Bondtech!

    • Nuno Santiago

      Hej Boyd!
      Thank you for sending us your very positive feedback.
      Great choice for high flow applications.

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