Four parts on TradeBase replace Trimview™ hardware: a 14.5mm concave window roller listed against 10kg rollers, a non-keyed window catch and spring for older windows, the catch spring on its own, and a spring-loaded nylon screen door bottom guide. The mix says a good deal about what goes wrong. Two of the four are catch springs, so the spring inside the window catch is the common failure, losing tension until the sash will not hold closed. Sashes drop when the concave roller wears, and screen doors wander off the track once the bottom guide gives up. Before ordering, measure the roller across its widest point, as 14.5mm is the identifying dimension and concave rollers of this shape are made in several diameters. For the catch, check whether the original is keyed or non-keyed — only the non-keyed catch is listed here.