Use these HOLZ or Drum O's to reinforce vent holes cut into your bass drum or floor tom heads. Easy to use, Just peel backing off the back circle, stick it to back side of your drum head in the location of your choice, used it as an easy guide to cut your vent hole, then simply snap the front circle on from the front. Done! Call us about special ordering custom colors (including red, green, purple, bue, and green) - call us for more info on this. The 2 inch model is sold in pairs of 2 each.