they are basically used to mount the electronic equipments in 19" enclosure systems.
very essential for applications where equipments need to be drawn outside the main cabinets frequently or even for maintenance.
1) alluminium three section ball bearing: support upto 70 kgs at full extension + corrosion resistant
2) ball bearing high quality in stainless steel: capacity : upto 30 kgs
3) made of ms : capacity upto 20 kgs