rusty-pie The plugs are definitely brass, and the thread was very easy to strip with minimal torque. Some of the plugs were almost hand tight, and the reason for leakage it’s pretty obvious to me: they have cylindrical threads (i.e. not conical) and seal by means of an rubber o-rings which is compressed axially by the plug head against its seat. These o-rings have hardened and shrunk with time/temperature and no longer perform their function. Designed to fail sooner or later in my opinion, as the sealing relies on a rubber which is not suitable for its purpose.
Using O rings isn't right for sealing, without thread sealant or PTFE the threads are bathed in water and unless the water is super pure, a galvanic reaction between stainless steel and brass takes place and the brass is sacrificed. Conventional heating elements in stainless steel boilers screwed in on the brass threaded piece fixed by teflon sealing washers also suffer from this, but the thread is much larger and thicker, so it goes unnoticed!
When you put the plugs in do it exactly as uncle Dave said, whether u use steel or brass. I thin k the threads are parallel threads not tapered and using tapered wouldn't be a good idea.
