Titanium backers for Voron V2.4 and Trident. these counteract the bi-metalic nature of frame and rails to create a flatter and more rigid frame 

From the Github:
"Due to different thermal coefficients of linear expansion between steel (rails) and aluminum (extrusions), the Voron V2 gantry forms a sort of giant bimetal temperature sensor element. This causes a warping of the gantry as it heats up with increasing chamber temperature."
more information about these here 

Kit includes:

• 2 x Ti backers pre drilled and ready for install on Y axis
• 1 x Ti backer  ready for install on X axis (on top for Dual MGN9H setups and behind for MGN12h setup) 
• ti screws for installation, you only need tnuts.