This additional extension coupler is for use with Harmer Modulock deck supports to increase height adjustment ability. Place onto the threaded rod and screw into place until you get the desired height. Each extension coupler is 125mm in length. What is Harmer Modulock deck support system? Harmer Modulock deck supports allows you to adjust the height of paving slabs, timber or plywood sheet decking to level out irregular, uneven or sloping surfaces so the spaces are more usable. Harmer Modulock is a raised pedestal system which also lends itself to concealed drainage, pipework, and services beneath a substrate and application for terraces, walkways, balconies and ballasted flat roofs. Complete with self-levelling heads that allow for a 5% gradient change, the heads have anti-noise and anti-slip rubber layers on their heads. Using Harmer Modulock deck supports to adjust the levelling of surfaces is extremely easy.