It deos look like UNC, walked into shop reachec for 1/4 UNC marked drawer, pulled out packet of two taps, checked that they were 1/4" and came home. At home I noticed that the taps are 1/4" UNF! dikeytyduckeytyfiqeyty. I "always" double check, it must be my specksavers moment or it's about time to have my head checked.
This really does not want to go together voluntarily.
Pekka