If you are running a 2-1/4" x 7" flame arrestor and want to use it with a Quick Fuel carburetor, you need this spacer so that the flame arrestor will sit properly on the carburetor.  Since the Quick Fuel carbs have adjusting screws for the floats on top of the bowls, the stock flame arrestor doesn't sit on top of those carburetors properly. We have sourced a custom-made spacer that lifts the flame arrestor just enough to clear the screws while still making a good seal on the top of the carb. We now use these on all of our Quick Fuel installations here at SCM. NOTE: You may need to machine the opening of the flame arrestor slightly in order for this to fit.  We use a Dremel tool with a sanding attachment to very slightly open up the bottom opening of the flame arrestor so that this spacer will fit properly.