from the website:
Powerflow systems are fabricated from a combination of 409 grade, 430 grade and 304 grade stainless steel. Material choice for each separate component (silencer casings, end plates, perforated pipes, tail pipes, etc) is made on the bases of suitablity, durability and cost-effectiveness, whilst always ensuring that the product is good enough for Powerflow and its dealers to cover it with a lifetime of ownership guarantee (for original purchasers). Silencers are produced using modern weld free techniques. All seams are mechanically formed to minimise material damage caused by welding and are completely gas tight. The tubing used in most Powerflow systems is 409 grade, which is preferred because of its superior malleability (bending) characteristics. 304 grade tubing is available as a customer option.
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Chris 'AKA' SuperRockin'MisterMagic!