Abstract: A subassembly for a downhole drill string has a hollow outer body or barrel with a plurality of blade openings. A plurality of blade sets extends outwardly through the openings. Fluid flow inlets are provided in the lower section of the body below the blade openings and flow outlets are provided in an upper section above the blade openings. An annular spaced apart support mandrel extends through the hollow section of body and supports and retains the blades in the openings. An annular fluid flow passage is provided through the annular space. Drilling fluids outside of the subassembly may flow through the inlet, up the annular fluid flow passage, and out the outlet thereby bypassing any plug or pack-off formed between the subassembly and the well bore. An existing subassembly may be retrofitted to provide a fluid flow bypass channel around the blades. The existing subassembly is provided with inlets below and outlets above the blades. The bypass channel is then formed between the blades.