Grommet is a type of grommets is mainly used for anti-vibration using or absorbing the vibration.
In order to customize grommets, we need to know these informations based on the above basic drawing.
A - Outter Diameter
B - Installed Diameter
C - Inner Diameter
D - Overall Thickness or Overal Height
E - Installed Thickness or The Thickness of board
R - Radius , if you are not ensure, also could be made.
Rubber is general term of materials, we could use lots of rubber for producing, but it should be mathed your needs.
You could choose Silicone, NBR, EPDM, SBR , etc.