Four 7/8" diameter 9 t.p.i. screwing taps, for nut fastener manufacture

Set of four 7/8" diameter 9 t.p.i. screwing taps, by Joseph Whitworth and Company, Manchester, Lancashire, England, 1850-1857. This is a set of four taps. First, the smallest diameter and most tapered tap is screwed into the pre-drilled hole. Then taps 2 and then 3 are screwed into the hole. Finally, the tapping process is finished with the largest tap with the most flutes. This is the finishing tap and should give a finer finish to the threads.