These Kendall Howard blank panels come in Flat & Flanged Spacer in 1U, 2U, 3U, 4U & 6U sizes. All Kendall Howard Flat Spacer Blanks have a high-quality black powder coat finish, rounded corners, and are Made in the USA. Filler Panels provide the most added strength, and mount with any rack hardware or use the built in Tool-less clips to snap them into cage nut style rails. They are cost-effective and simple to install.