The Whiteside HMA12 Screw Type Helix Mortise Cutter Arbor is for use with Whiteside's Helix Mortise Cutters (sold separately). Can be used in either hand held or machine routers. Arbor has a 1/4-28 end thread size. Whiteside Machine Company - Claremont, North Carolina.
SH = Shank size TH = End Thread size. OAL = Overall Length.
1/2" SH X 1/4-28" TH x 1-3/4" OAL