These are the SLS-printed nylon plastic parts, which are meant to ensure that the LGX FF Flexibles Add-On kit fits well on a Prusa i3Mk3 3D printer. For a full upgrade on your Prusa i3Mk3 you'll also need the Bondtech LGX eXtruder and the LGX FF Add-On.
The Bondtech LGX™ Adapter Kit is supplied with:
Find the LGX FF Add-On HERE.
Find the Bondtech LGX Extruder HERE.