The use of blockwork allows structures to be built in the traditional masonry style with layers (or courses) of staggered blocks. Concrete blocks may be produced with hollow centers (cores) to reduce weight, improve insulation and provide an interconnected void into which concrete can be poured to solidify the entire wall after it's built. Blocks come in modular sizes, with the most popular typically referred to (by their thickness) as "4-inch", "6-inch", "8-inch", and "12-inch". In the US, CMU blocks are nominally long and wide. Their actual dimensions are less than the nominal dimensions (to allow for -inch mortar joints between blocks in any orientation). In Ireland and the UK, blocks are usually excluding mortar joints. In Australia, New Zealand and Canada, blocks are usually excluding mortar joints.