The Knightsbridge Screwless 10A 1G 2 Way Light Switch Polished Chrome is used when you have three switches controlling one light. An example of this is on a landing ,there is a switch at the bottom of the stairs, one at top of the stairs and one at the end of the landing. On this circuit you would need the middle switch to be intermediate (i.e. the one at the top of the stairs) in order for all the switches to function properly.
The Screwless Switch is made from high quality ultra slim, premium grade material and comes complete with integral gasket. The Knightsbridge Screwless units are compliant to all relevant British safety standards and has a Minimum mounting depth: 16mm.