FMF Racing Q4 Hex Aluminum Slip-On Muffler w/Stainless End Cap for KTM/Husqvarna 16-19 ModelsFMF Q4 HEX S A Slip On Exhaust KTM Husqvarna 250cc 501cc Loud pipes might save lives on the street but in the dirt sound is the number one killer of riding trails and regulated track hours. If you have been searching for a performance enhancing muffler that does not wake the dead, then the FMF Q4 HEX is the muffler for you. FMF approached the design process of the Q4 HEX with the goal of achieving more power, while keeping noise levels to a minimum.