siafast is the brand name for hook&loop style discs. This disc is made out of the same Silicon Carbide material as the 1749 7" disc, but it is very easy and quick to exchange thanks to the proven hook&loop system. 5" discs can be used on the same backup pad that you use for the diamond pads. It is basically foreseen for dry application, but you can also wetsand if you only moisten the grit side.