Now you can get the small size of the RLV Mini 91 Muffler in a 3/4" NPT screw in muffler. Increase your performance and get the classic RLV sound with this free flowing muffler. Screws into most of our 1" OD headers that have flanges. Approx diameter of 1-5/8" Approx length of 5-1/2" Please note that NPT threads are tapered threads and will not screw all the way into the female fitting. A tapered thread seals as it is tightened