Section R. 408.10115 - Machine spindlesRule 115.
(1) A wheel or flange that is secured by a spindle nut shall have the direction of the thread opposite that of the spindle rotation so that the nut will tighten as the spindle revolves.(2) A spindle shall be long enough to engage all the threads within the nut.(3) Spindle threads shall extend inside the flange, but not more than halfway within the hole of the abrasive wheel.(4) The spindle shall not be larger than the nominal size, with the undersize tolerance limited as required to prevent a hazardous condition.(5) A spindle on which a threaded-hole wheel is mounted shall be threaded to allow the abrasive wheel to be screwed flat against the back flange. In addition, all of the following requirements shall be complied with: (a) The direction of the thread shall be such that removing the abrasive wheel requires rotation of the wheel in the same direction that it turns when in use.(b) A spindle shaft shall not touch the bottom of a blind hole in an abrasive wheel.(c) A back flange that is specified in this rule shall be flat, unrelieved, and square to the spindle axis.Mich. Admin. Code R. 408.10115