Threaded flanges are made by machining the inner bore of the flange into a pipe thread and connecting it with a threaded pipe. It is a non-welded flange.
The advantage of a threaded flange is that it does not require welding, and the additional torque generated on the barrel or pipe when the flange is deformed is small. The disadvantage is that the flange is thick and the cost is high. Suitable for connection to high pressure pipes.