Bondtech Prusa I3 MK2.5S/MK3S Slice Mosquito Extruder upgrade

Bondtech Prusa I3 MK2.5S/MK3S Slice Mosquito Extruder upgrade

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Bondtech Lightweight Upgrade Kit for Prusa i3 MK2.5S/MK3S

 Must Have (S) Variant will not work for MK2.5 or MK3

X-Carriage Upgrade is Required for this upgrade it is not included.

Or you can print your own using these links.



This Upgrade Kit does not include the gears (already supplied by Prusa).
This upgrade does NOT include a Mosquito hotend.
This Upgrade Kit requires extra parts to install (X-Carriage Kit).
You can buy it from us or you can download the STLs and 3D print them. Check download links in the Resources section.

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 kit With Optimized Design to fit Mosquito hotends

This is a Bondtech upgrade for the popular Prusa I3 MK3S and MK2.5S that will allow the use of the world acclaimed Mosquito hotends.
Bondtech Extruder For Prusa i3 MK2.5S & 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.

Upgrade Your Extruder
Increase the gear ratio of your extruder to a 3:1 that will deliver extra push force and higher resolution.

Print Faster Or Better
With this lightweight extruder that saves 15% of the weight of the parts replaced, it is possible to 3D print faster or to improve the surface quality when printing at the same speed.

Reduce 3D Printing Issues
Improving material extrusion will decrease the risks of encountering 3D printing issues. Avoid heat creep and reduce clogs. Get a regular and precise material feeding with no slipping neither filament deformation to minor under and over extrusion caused issues.

Upgrade kit With Optimized Design
The Bondtech for Prusa i3 MK3S is the latest upgrade kit from the Swedish manufacturer that incorporates all improvements achieved with the help of the Prusa community.

Bondtech Extruder For Prusa i3 MK3S
This kit contains all the parts needed to convert your printer's extruder to the popular Bondtech BMG (Bondtech Mini Geared) based design. Its 3:1 ratio increases the accuracy and resolution of material extrusion. Its carriage printed with PA12 by the SLS process and with updated geometry optimizes the hotend’s heatsink cooling.

Lightweight BMG (Bondtech Mini Geared)
This upgrade saves 15% weight of the extruder. This reduction will have meaningful impact on the moving weight and vibration thus lowering the ghosting effects.
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’s 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.
However, you also have the option of using Slice Engineering Mosquito thermistor and 50W heater.
We recommend the 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.
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.

What’s in the Box

  • 1x Extruder housing with Hinge, Hinge shaft, and main shaft assembly.
  • 25mm pancake Stepper Motor
  • Extruder Motor cable in a plastic bag
  • Screws and nuts in a plastic bag
  • Powered by Bondtech sticker
  • 5x 3D printed parts
  • 5x Zip Ties

Reducing 3D printing Issues
The new housing design improves the heatsink cooling and lowers heat creep issues that are associated when all metal hotends print with PLA. This enhancement is meant to avoid PLA clogs.
The higher push force drastically reduces slipping, shredding and filament deformation and works to avoid the common filament 3D printing issues that are caused by under and over extrusion.

Updating the Firmware
To use this upgrade in the MK3S, there is a need to update the firmware. The e-steps value must be updated to 830.

Additional Information

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

 Weight Reduction
343,2g of parts coming out and 291,5g of parts coming in. A 51g (15%) weight save.

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

Technical Datasheet
Article number : EXT-KIT-68
EAN code : 7350011410651
Net weight : 291,5g
Gross weight : 380,2g
Package Size : 137x94x65mm
Gearing ratio : 3:1
E-steps value : 830
Extruder Housing: SLS Printed parts in PA 12;

we do not do firmware support please edit your settings/load firmware at your own risk

Note! This firmware is for Mk2.5s and MK3s users with the new filament sensor.

The firmware is based on newest stable version of Prusa-firmware and support MK2.5s and MK3s users with a Bondtech extruder.

Bondtech specific changes:

Estep set to 830. (415 for MK2.5s)
Adjusted Z_MAX_POS 205 to allow Z and XYZ calibration.
Changed printer name.

Download the firmware here: