NOTE:  The Seimitsu screw-on pushbuttons in 30mm now come with solid black screw-on nuts

Seimitsu clear pushbuttons were the first on the market and has the most color variations on the market today.  These are 30mm pushbuttons that are the screw on type, which with each pushbutton a nut will come with it to tighten the pushbutton.  Screw-on pushbuttons are great for custom modding controllers that vary in the depth of the control panel.  Custom art can be inserted by removing the inner cap

The size of these pushbuttons are the standard main play buttons on many commercial controllers out there, from Hori, QanBa and Mad Catz.  If you are thinking of custom making a all-button controller, generally, 24mm pushbuttons are used for that purpose