Standard lengths are available in 150mm increments.
The SWL (safe working load) is based on the total UDL (uniform distributed load) over maximum span using 150mm end bearings
To achieve the CH & CX loading figures indicated, lintels must be built-in as illustrated, ensuring that the blockwork infill is well-jointed during construction and compatible with the strength of thr masonry above.
When using the Catnic CH and CX Open Back ranges with concrete floors, always ensure that the blockwork is built tight against the inner vertical face, and that a mortar joint is added to the top of the blockwork so that the floor units have an even spread over the inner flange of the lintel.