harbor freight drain cleaner 4 piece bit set fits all harbor freight drain cleaners drain auger specialty bits new hydrostar drain monster drain cleaner 4 piece bit/cutter set. you will find this set to be a much better set than what the hydrostar came with. if you need the metric screw that holds the bits onto your cable end, the size is (m6 x 1) or you can simply tap the cable end to (1/4 - 20) and use a standard 1/4" coarse thread bolt. both are very close in size.