Thanks guys, to me It just feels wrong, the washer they supplied doesn't fit to the base of the thread and the nut only fastens half way down. So to make it work i need to file out the inside of the washer, pack it out with more of my own washers and tape the hell out of it. Whoever invented standardised tapered thread is a jerk but i will confirm with supplier if this is actually made to spec.
Ps the pic is oriented correctly, it is a weldless thermo placed face down on a flat surface taken side on with a tripod. also im pretty certain it is not brass, that's probably just the lighting in the photograph.