inverted u shaped configuration and of a size to fit inside the runner primary channel 18 the top side of the cartridge 20 includes two spaced apart mounting apertures 32 so that when the cartridge 20 is positioned in a desired location along the channel 18 it can be secured using self tapping screws 34 extending through the apertures 32 and into slot 36 such a configuration means that the roller cartridge 20 may be fitted to the runner 14 without the need for drilling typically each shelving unit will include a roller cartridge 20 at the longitudinal ends of each runner 14 however there may be circumstances where more are required and the runner primary channel 18 may accommodate for this the roller cartridge 20 includes larger co axially aligned apertures 60 extending through its side walls a pin 62 which extends through the apertures 60 is used to maintain a roller 69 inside the cartridge 20 the roller 69 is rotatable about the pin 62 and allows the runner 14 and hence the shelving unit to move relative to the track 12 as will become apparent also mountable to the runner 14 are end brackets 38 as mentioned not only are.