We've found that in some situations, there's a bit too much room for the pad in Wilwood's Powerlite calipers. Not enough to cause a functional problem or a safety issue, but just enough to cause a clunking noise as the pads shift back and forth. If you've installed a set of Powerlites and you have a clunk when you get on the brakes, there's a good chance this is your issue. We already include extra plates with any applicable kits, so these are in case you lost those or have extra lose pads - in other words, you'd generally purchase these reactively as opposed to proactively. Includes four plates, which is typically enough for one axle / two calipers, although that can vary from pad to pad. Stainless steel for long life. Wilwood part number 300-5875, also used on Dynalites from our old Big Brake Kits as well as other calipers we haven't used in the past. Not used on our current BBK Dynapro calipers.