dropdown heading not selectable

I have a drop down with items and prices. Pretty basic. Is it possible to have a heading category that is not selectable, but item and price would? This is what I'm talking about.

Dropdown items:

  Carriage bolts //Category heading not selectable

  1/2" x 3/8"

  1/2" x 9/16"

  etc.

  Hex bolts //Category heading not selectable

  1/2" x 5/8"

  etc.

  Zinc Flat Washers //Category heading not selectable

  3/8" (bolt size)

  etc.

Would it be possible via javascript? Or, at all? Can someone chime in and let me know. Thanks.