The 5/8 Inch Dado Arbor that is used to hold the Dado Head to make any width Dado, Rabbet, or Groove cut you need. Fits MARK 7 and all other MARK V models. Having extras allows you to have a variety of tools ready to go to work on a moment's notice without bothersome change-over. Note: Cannot be used with regular 10 Inch saw blades.