Review on 📏 High-Performance Aluminum Sheet - 1&#34 by Robert Farrar

These are just the right dimensions for NPT plugs. Some reviewers seem to be misinformed about how the NPT diameter is measured. Due to the bad reviews I thought the forks might be mislabeled but after receiving them they are fine. I used a 1/8-27 NPT threaded tap (pre-drilled 23/64 which works best for my application), applied some Permatex high temp thread sealant to the threads and it worked great. So: A 1/4 NPT male has an outside diameter of about 3/8 - which is just right. Installed to cover the regulator hole in my aluminum v-twin engine block instead of using a big chunky bolt. It's a bit pricey and took a while to arrive but they are high quality and I will be ordering more.