HANNO
British BSW ( british standard whitworth) threads will interchange with UNC American threads ..... BSW has a 55 degree thread angle and UNC is 60 degrees.. but for practical purposes .. they fit OK ..
EXCEPT for the 1/2" size ..this size has different TPI threads per inch .
The BSF .. (british standard fine) threads are found on British MAKES .... my Morris has them everywhere ... along with metric threads on the motor
.
Mike