This is an 8-1/2" deep sleeve that is put into place by the electrician prior to the concrete being poured and it comes in varying widths. After the concrete sets, conduit is run through the sleeve to run risers from deck to deck. If a pour is deeper than 8-1/2", then the user will use two or more stacked together to do the job. They are made from a slippery plastic and are usually a forest green color. You would order them in sizes from 1-1/2" through 6". A 4" Crete sleeve would allow a 3" pipe to fit inside.