The Fulterer FR5400.L, 54″ Heavy Duty Locking Drawer Slides, (550 lb. Class). This 54″ model has a static weight capacity of 374 lbs. or 170 kg.. Please note: The Lock handle protrudes an additional 1-3/8″ (35mm) longer than the length of the slide itself.
It can work as a lock-in only, or lock-in and lock-out drawer slide depending on the orientation of the slides. All you need to do is swap the left and right sides and the locking mechanism will operate in the other mode.
The slide rails are made from cold rolled, galvanized steel and have stainless steel ball bearings with plastic bearing cages to reduce noise. Price is per pair, screws not included.