Rack mounting the Elektron gear is a person choice. IF you wanna do it, you need these slices of metal with holes in them. or your own Foundry or Silversmith. i have no metallurgy skills so i purchased these.
they are great, but seem overpriced considering i could probably have made 50 of them for that price in Bangledesh.
Still, the job is done. they work. go for it.