The Briggs & Stratton 590566 is a Muffler Guard (also referred to as a muffler shield or grade muffler) used primarily on small vertical shaft lawn mower engines. Current Availability This part is currently listed as discontinued or inactive by several major parts distributors, including Sears PartsDirect and Scag Mower Parts. New Old Stock (NOS): You may still find it at retailers like Jack’s Small Engines for approximately $12.75, though stock levels fluctuate.