BSW/ BSF/ Whits threads are used where clerance between male & female threads is to be controlled. This uses Imperial system of units.
Specification
• Basic Dimensions- BS 84-2007 & Gauging Practice: BS 919 Part II - 2007.
Manufacturing Range
Thread Plug & Ring Gauges from Diameter 1/8 to 6" , TPI 40 to 2.5