Four parts here replace Robb & Brown™ sliding door and window hardware. Three are rollers: a pair of 25kg adjustable patio door carriage and roller assemblies that also suit Dowell®, Nu-Lock™ and Lidco® doors, and a 38.4 x 18.9mm adjustable carriage and roller for the Series 40 sliding door. The fourth is a non-keyed window catch and spring, which also covers Frontline™ springs. Rollers and catch springs are what go on these frames — the wheel wears flat or the carriage adjuster strips, and the catch spring loses tension so the sash no longer holds shut. The 38.4 x 18.9mm figure is the identifying dimension for the Series 40 carriage, so measure the old carriage body rather than working from the door. On the patio rollers, confirm the panel weight sits within the 25kg rating.