Brake kits, load cell upgrades, springs and face plates for the pedal set in your build.
Upgrade kits change how a pedal feels without replacing the whole set: stiffer springs or elastomers for a firmer brake, load cell conversions, or longer pedal faces for a different heel position.
Pedal accessories are almost always brand specific, so this page shows parts from the same brand as the pedals in your build.
A spring or elastomer upgrade kit usually costs €20–€60 and takes a few minutes to fit. A load cell conversion kit, which replaces the pedal's sensor rather than just its feel, costs more and may need the pedal's companion app to recalibrate afterwards.