***Please read before you make your purchase*** EXHAUST DOES NOT WORK ON DUROMAX ENGINE 16HP OR 18 HP DO NOT ORDER IT IF YOU HAVE ONE OF THESE ENGINES! 1" Pipe Thread... 1" does not mean the actual size of the outside diameter... read at the bottom of the page to understand how to measure threads, Each thread size has a defined number of threads per inch (TPI). Erect Muffler Exhaust Pipe 1" thread for: Predator 301cc, Predator 420cc, GX 270, GX Honda 390 see photos for better details. Includes hardware & Gasket Finding the Correct Pipe Thread Size National Pipe Threads (NPT) Pipe sizes do refer to physical dimensions, but the plumbing industry standard for the sizes of pipe is not always as straight-forward as measuring the pipe. Measuring the pipe will oftentimes mislead you into choosing the wrong pipe, so do take care. The "pipe thread size" as shown in column 3 of the table below is measured and based on the inside of the pipe. But, to actually determine the size of a pipe, the outside diameter of each pipe or fitting must be measured and compared to the table for size identification. For example, a 3/4" NPT pipe thread has an outside diameter of 1.050 inches. Each thread size has a defined number of threads per inch (TPI). The 3/4" NPT pipe thread has 14 threads per inch. Both the TPI (threads per inch) and OD (outside diameter) of the thread are required for positive identification of thread size because several sizes have the same TPI. pipe thread specifications -Engine not included. Center hollow to hollow 2" (please look all The picture for details) This been tested on 8HP (301cc) OHV predator, and Predator 13 HP (420cc) Works also: GX 270 & 390, Briggs 1450 305cc, Lifan LF190F-BQ 15 HP 420cc Made in U.S.A.