A grit removal unit for a waste water system, including a round grit removal chamber with an input for waste water and an output, a grit storage chamber beneath the grit removal chamber, and an opening between the grit storage chamber and the grit removal chamber. A vertical drive shaft extends through the grit removal chamber into the grit storage chamber, and is rotatable to facilitate waste water flow in the grit removal chamber whereby grit in the waste water is directed toward the opening. A grit size restrictor includes a shear secured to the drive shaft for rotation therewith (the shear including a plate extending radially from the drive shaft above the opening), a first set of bars extending across the opening, and a second set of bars secured to the bottom of the shear plate with the second set of bars positioned adjacent the first set of bars.