Tradies use these “clean out” blocks as the first course on the bottom row of a concrete block wall being constructed that will be core filled with concrete, allowing the tradie to observe when core filling has been achieved correctly. These blocks are often referred to as being 400 x 200 x 200mm in size because the mortar width is also included in that measurement, and it is easier to work out bulk quantities required. The actual size is 390 long x 190 wide x 190mm high. An optional 10.34 block can be used for added support of the wall under construction.