Tips from Rachel: The plastic washer is NOT absolute necessity for grommets.
Only when your material is too thin or some other special material, which you feel grommets are not immobility enough on your material, then you can try to choose add one plastic washer between the grommet and the brass washer. It may make your grommets more stable on the material. ( Instruction in the picture.)
Sold in 100 PCS per pack.
1.) Color: White
2.) 11 sizes are available.
Tips: 1mm=0.03937inch
3.) Material : Plastic
4.) Required Tools (sold separately on our store):