Bondtech Upgrade Kit - BMG Extruder - Prusa i3 MK3S+/MK3S & MK2.5S





Upgrade Kits


Prusa I3 MK3S Extruder upgrade

EAN13: 7350011410651 SKU: EXT-KIT-68 Categories: , , , , Brand:

Prusa I3 MK2.5S / MK3S / MK3S+ Extruder upgrade IDGA

(1 customer review)

This kit ships with BMG IDGA!

featuring the 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 3D printers, featuring an optimized design achieved with the help of the community.

This upgrade kit is compatible only with the original All Metal V6 hotend that is supplied with each Prusa.

Product Main Features

This extruder upgrade kit is for the Prusa i3 MK2.5S / MK3S / MK3S+.

  • Adapted to fit Prusa’s new filament sensor;
  • Includes one Bondtech’s 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.



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Upgrade Your Extruder

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

Print Faster Or With Higher Quality

Use a lightweight extruder that will allow your 3D printer to print faster or to achieve better surface quality.

Reduce 3D Printing Issues

Decrease the risk of heat creep to avoid clogs and improve filament feeding to avoid slipping and deformation that cause under and over extrusion issues.
For even more effective HotEnd cooling we recommend a fan with high pressure like Sunon’s MF40100V1-1000U-G99 or similar.

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.

Upgrade kit With Optimized Design

This is the latest generation Bondtech upgrade for the popular Prusa I3 MK3S, with an optimized design achieved with the help of the community.

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.
It is also compatible with the MK2.5S model.

Lightweight BMG (Bondtech Mini Geared)

With this version we also lower the moving weight to reduce ghosting and vibrations or to allow increasing the printing speed. 15% of weight saving was achieved.

Addressing 3D printing Issues

The enhanced housing design improves cooling and decreases heat creeping issues that all metal hotends have when printing with PLA. This small enhancement will avoid many clogs.
The increased push force will drastically reduce slipping, shredding and deformation of the filament avoiding most of the common filament 3D printing issues that start with under and over extrusion.

Updating the Firmware

To use this upgrade in the MK2.5S / MK3S / MK3S+, the E-steps and Z_Max needs to be updated. Check out the latest version of our firmware here.


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 395 g
Dimensions 15.5 × 11.5 × 10.5 cm


This Upgrade Kit includes a new Bondtech IDGA (Integrated Drive Gear Assembly). Use the secondary drive gear that came in your Prusa.

This Upgrade Kit requires an x-carriage kit to be installed.
You can buy the x-carriage for the MK3S from us or you can download the free STLs models and 3D print the x-carriage parts available also for the Prusa i3 MK2.5. Use the “Download STL files” option of our “Firmware & More” menu to reach the download links.


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

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

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

00. Bondtech Prusa i3 – Firmware Update

Technical Specification

  • 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 : 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°C

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.

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

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


Bondtech Github. Contains Step file, 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.

MMU2S Add-On files

We have available the following sets:

1 review for Prusa I3 MK2.5S / MK3S / MK3S+ Extruder upgrade IDGA

  1. Deividas Adkins (verified owner)

    I’ve had my Mk3S for over two years and this upgrade has made it the perfect printer now. Bye bye to heat creep! With a 0.9 degree motor I have never had better-looking and more consistent extrusions. I’m so glad I went with the genuine upgrade as opposed to the aliexpress knock-offs. I couldn’t be happier.

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