there is a big difference in usage between home racks, an old kitchen device, and technologic "rack and pinion". Above categories will be quite diferents !!!
I deleted the categorisation to Fireplaces. In French, "cremaillère" means a tool, crémaillère-shaped, to hang the cauldron above the fireplace (Walloon crama (this : Crama.jpg) => these "crémaillères" are located in category "Trammel hooks" which is categorised in "Fireplaces".