Product Description Flange is CNC cut from heavy steel plate to prevent warping, outlet pipe is SS NPT 1" pipe thread. Flange center hollow to hollow 1"968 = 50mm (see photos for details) 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 1" NPT pipe thread has an outside diameter of 1.308 inches. Each thread size has a defined number of threads per inch (TPI). The 1" NPT pipe thread has 11.5 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. PRODUCT INFORMATION: Model:OT001132 Item Weight: 0.33 pounds Package Dimensions: 7.48 x 5.12 x 2.36 inches Item model number:1" Threaded Exhaust Flange