Tracy Tools sells taps and dies in 1/8 x 48 BSF so it must have existed at some point — and indeed still does in this instance — but not in today's thread charts. Their stuff is usually good quality at a good price so worth buying to complete the set, if you would ever have any use for that size.

Edited By Hopper on 07/06/2022 07:06:08

Tap and Die Co List 1/16 x 60, 3/32 x 48 and 1/8 x 40 and from memory, when describing a steam donkey pump in a 1930s ME, LBSC mentioned an 1/8 x 60 'from brer Kennion'

The smallest standard Whitworth threads are indeed as you list:

1/16 inch X 60

3/32 X 48

1/8 X 40

So are not arcane specials.

(Source: Bentley, W, Machine Shop Companion, The Bentley Publishing Co., 1913)

That book also gives useful change-wheel tables for cutting inch- and with 127T wheel, mm- pitch threads from a 4tpi lead-screw; which is that of the Harrison L5. Though of course useful to me only if my lathe's wheel set matches the tables!