This self-levelling head for features 20mm x 3mm tabs to align and support slabs, timber and decking when installed over the top of Harmer Modulock deck supports. 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.