What is my bicycle flange nut size? As stated in my previous question, I am still trying to find the size of my flange nut on my seatpost. I need a new one because the old one was worned out. I bought a 3/8-16inch g/8 flange nut off of ebay and it was way too big for the bolt. I have reposted the pictures over here and hoped that someone can help me determine the flange nut size and where to buy it. Btw, due to covid19, I am trying to stay home so I hope to be provided with online help. Thanks to those who previously answered my question and I hope for more answers here. Any answers or comments with be appreciated. Thanks!
The thread pitch looks too coarse to be metric. Since a 3/8-16 (3/8 inch diameter with 16 threads per inch) was too large I would speculate its' a 5/16-18 (5/16 inch diameter with 18 threads per inch). The standard wrench used with this size nut is 1/2 inch. This is a common size on older American made bikes.