Are you sure these are taps, may be they were use as thread cleaners/chasers …but then you would use ordinary taps in that case… ?

George.

Do you have the facility to photograph one of these taps in detail?

My guess is that they are [as you say] flat; and will therefore be 'zero rake'

… That would make them O.K. for use on hard leaded brass, bur risky on steel.

MichaelG.

They sound something similar to Threadflo taps, these are slightly triangular, with no flutes, they are good in brass, aluminium, and stainless steel, the tapping hole is a little larger than for a conventional cutting type tap, as the thread is formed rather than cut, and no metal is removed in the forming of the thread.

Ian S C

A while back I purchased a watchmaker's lathe. Included with it were some very small taps. They had no flutes but had some flats ground on them. The flats are not parallel, resulting a starting taper on the end. I guess that would work in soft metals like brass. I would like to hear from the clockmakers on this forum. Is this kind of tap common?

They look a little bit like Taptite screws, which are also(?) thread forming rather than thread cutting. They aren't recommended for reuse and in practice they do make a little swarf but can be driven directly into diecast holes without any machining required.

Edited By Muzzer on 17/09/2016 23:34:37