what is a water thread and where is it located

 

water thread... ummm, there are water jacket seals in the internals of the motor...?

 

It's where the water threads through the engine to seal it properly duh, didn't you know that

In all seriousness, though, if you're talking about the water jacket seals they are found between the irons and rotor housings of the engine, one outer and one inner.