Stainless Glasspack Muffler (4-Inch Straight-Through Body) A glasspack that isn't disposable. Most glass packs — Cherry Bomb, Thrush, the cheap stuff at the parts store — are aluminized steel that rusts out and blows its packing in a season or two. Ours is built from 409 stainless steel, so you buy it once. You still get the aggressive, higher-pitched straight-through tone a glass pack is famous for — you just don't have to replace it every year. The 4-inch round body flows straight through for a loud, aggressive note, comparable to a Carven, Flowmaster, or MagnaFlow 4-inch muffler but at a direct-from-the-builder price. It's the most aggressive muffler we make. It also doubles as a resonator, and because it's a true straight-through with a real muffler body, it's a popular way to get near-straight-pipe sound while still passing a visual inspection. Specs 4-inch round body, straight-through glass pack (glasspack) design 409 polished stainless steel — won't rust out like aluminized packs 2.5-inch or 3-inch inlet and outlet, center-to-center Your choice of weld-on or clamp-on Reversible, universal fit for any custom exhaust build Made in the USA Not sure on size? Match the inlet/outlet to your exhaust tubing — 2.5 inch for most V6 and mild V8 setups, 3 inch for bigger V8 and high-flow builds.