Features: BSW - British Standard Whitworth; The angle of thread is 55 degrees as opposed to 60 degrees in Metric and Unified threads. ; This thread form was developed by Sir Joseph Whitworth in 1841. ; The thread form has rounded roots and crests and is specified in BS84:1956. ; BOTTOMING TAPS have a lead of two threads and are used to ensure minimum thread run-out when tapping to the bottom of a blind hole. Bottoming Taps are typically preceded by the use of a Taper or Intermediate Tap. ; INTERMEDIATE TAPS have a lead of four threads and are used in most general purpose applications to cut a thread true to a pre-drilled pilot hole. ; TAPER TAPS have a lead of eight threads and are used as a starting tap in difficult or high precision holes. ; Specifications:Diameter1-3/8"Pitch6 tpiLeadSetOverall Length162 mmTapping Drill30.5 mm