The mortar-free, ProVantage Glass Block Installation System consists of 38 in. (40 in. nominal) horizontal spacers, 7.25 in. vertical spacers and either an anchor and expansion strip or a 3 in. W Clearly Secure brand U-shaped perimeter channel. Spacers are positioned between each glass block and held in place with REDI2BOND glass block silicone. The ProVantage anchor or U-shaped perimeter channel is used to fasten the glass blocks to the project's sides, sill and header. Depending on the project, the joints are finished with either grout or REDI2BOND glass block silicone. Each component is sold separately. These spacers are made specifically for 3 in. thick glass block, not to be used with 4 in. thick glass block.