This is not true, because most homes are built before 1998. The vendors you name had other threads prior to 1998. This also causes a lot of trouble because "old

This is not true, because most homes are built before 1998. The vendors you name had other threads prior to 1998. This also causes a lot of trouble because "old" and "new" does not match, even when from the same vendor. The only way is to change the valve (very expensive) our buy extra adapters. This is also true if you break an existing thermostat: You can't purchase them anymore. You'll have to buy one of the "new" standard and pick on of the "solutions" mentioned above. For example I'm living in an early-1990s building equipped with the old Oventrop M 30 x 1.0. I just bought a smart thermostat which claims to be compatbile with Oventrop but turned out only with the post 1998 Oventrop M 30 x 1.5 …