12" MDF Speaker or Subwoofer Spacer Rings Case Pack. Each Kit Includes; ( 3 ) Pack of MDF Rings; ( 1 ) Gorilla Glue (glue size will vary). Easily add 3/4" Spacer for Custom Installation. Fits all 12" Speakers and Subwoofers. Made from Heavy Duty 3/4" MDF. Easily Paintable or Primed. Inner Dimensions 11"; Outer Dimensions 13" See Picture for detailed dimensions.