Features: BSF - British Standard Fine; This thread form was based upon the British Standard Whitworth (BSW) but has a finer thread (more threads per inch for a given diameter). ; The thread form was first introduced in 1908 and is specified in BS84:1956. ; When used on external threads this series has greater tensile stress area than coarse threads of the same size. ; Fine series threads will resist stripping out better than coarse threads in areas where the external and mating internal threads are subjected to loads equal to or greater than the capacity of the screw or bolt. ; Fine threads are also used where the length of engagement is limited or where wall thickness demands a fine pitch. ; 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:Diameter9/16"Pitch16 tpiLeadSetOverall Length91 mmTapping Drill12.8 mm