Review on Oatey 33403 4-Inch Plastic Plug with Galvanized Screw and Wing Nut by Michael Adams

70 year old cast iron breather was unthreaded, brass cap could not be unscrewed. The hole was just under 4 inches, I measured it at 3-7/8 inches. This lid fitted perfectly with just a few turns of a massive oversized wing nut. The best part is that if I ever need access, it's easy to remove. The flush port is on the top of the U-trap so it's not pressurized and the water normally never makes contact with the cap, so I have no idea if this cap will hold up to pressure. This 4 inch cap replaced a brass cap that is marked 3-1/2 but actually measures 3-7/8 to the outside edge of the threads. I don't know how plumbers manage to keep track of all these weird dimensions. Best of all, this connector was a lot cheaper than the alternatives, a third the price of a Czerne connector, and it fits better and is more convenient to use.