If you have an older version of the HUDORA BigWheel Air Dual Brake (Article 14015) and would like to replace the brake unit, please note the following:
The brake system has since been updated, and the attachment now features 6 holes instead of the previous 4.
But don't worry! You can still retrofit your older model with the new brake system.
For the conversion, you will need:
A new rear wheel (available here)
A new brake unit (available here)
Two washers, which are not included with the rear wheel or the brake unit.
In the image below, you can see the location where the washers need to be installed: