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



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

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.

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.

Available on backorder

  • 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.



    This Upgrade Kit does not include the Bondtech drive gears (already supplied by Prusa).

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

    Optional items:

    For MK2.5S Users:
    The Mosquito HT Thermistor is not compatible with RAMBO 10a/13a mainboards.
    Do not use this option if you have a Prusa i3 MK2.5S.


    Product Main Features

    This extruder upgrade presents the following main features:

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

Additional information


Compatibility table


These are the guides that apply to the Bondtech Upgrade Kit for Prusa i3 MK3S/MK2.5S With Mosquito Interface

01. Prusa i3 MK2.5S / MK3S Upgrade Kit – Strip Reusable Parts

02. Prusa i3 MK2.5S / MK3S – Mosquito Upgrade Kit – Installation

00. Bondtech Prusa i3 – Firmware Update

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;


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 Stepfile, installation manual, exploded view, and others.

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.


Find and download the firmware here:

MMU2S Add-On files

We have available the following sets:

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