I can only offer the obvious comment that they look like a pair - the upper one would be the one to use first, as it has a plain section to locate in a hole of matching size. The lower one is a 'bottoming' tap which would work down to the bottom of a blind hole.
I've never seen any quite like them, certainly not in brass + steel together. Do you have a matching die? Where did they come from?
No Dies sadly. I got them from a clearance of a Woodcutter's property (I work in tandem with an auction house). What is of interest I feel is the 'roughness' of the casting yet the relative accuracy of the boxwood tube holders. I have frequent finds like this & have several items that I'd be pleased to have identified.
The only threading designs I know are either hollow pipes, where the shaving disappears into the pipe from the cutter(s), or the (more familiar) "pineapple" style where longitudinal grindings create both cutting edges and clearance.
I'm not sure where the cutting edges and/or shavings clearance is on the items shown.
And brass is very soft - tapping holes this big involves high forces.
However .. whilst on the subject of taps, the thread & pitch looks reminiscent of that used internally in an old bathroom tap (for raising / lowering the washer), so maybe they were for removing gunk and lime scale from the tap internals with no danger of damaging the existing thread.
Interesting - what size are the "taps"?
Think I agree with the other posters who query whether these are actually taps, because of the lack of anywhere for the chips to go. And given the nicely finished boxwood holder, would have expected any corresponding die to have been in the same case. Maybe a thread cleaner, but .....
Out of interest which bit of Scotland throws up interesting things like this?
Doesn't seem to be much of interest up here in the North East "cold shoulder". Though for the real car boot afficianados, there is a Typhoon ejector seat in the collective sale near Inverurie tonight