The default enclosure kits come with cheap plastic knobs, which work perfectly fine, but don't look nearly as cool as these knobs. They're made out of a dark steel with knurled grip and look fantastic next to the black hardware. The pictures show it on the FT-5 model, but they are compatible with any enclosure.
Be sure to order the number of knobs for the kit you're buying. For example, the FT-5 has 4 knobs and the CR-10 uses 1.