We started using these on our crate and test motors for protection during storage and shipping, and found they were so handy that we decided to start offering them as a convenience. They are a plastic formed "hat" or cover which fits over the carb and seals all dust and debris tightly out. These work great with Holley 4150 carbs, or any carbs with a 5 1/8" neck. A small detail that is often forgotten. We also carry other carburetor essentials such as gaskets, return spring kits, fuel lines, etc.