UNF/NF threads

[philthehill]

Just a reminder that UNF and NF threads are slightly different in that the root and tips are not the same. It does mean that the threads are not fully interchangeable.
I am reminded of this difference as I have just tried to fit a bolt into a thread marked 1/2" x 20 TPI which would not fit. Both 1/2" UNF and 1/2" NF are 20TPI. The result was that I had to purchase the correct tap/die.
If the thread is tight but marked as either UNF or NF it may be that the TPI is right but the form is wrong.
Never force a thread be it either male of female - investigate what is wrong.
In relation to the Morris Minor it is important and to that end - BMC inserted into the Morris Minor wksp man BMC general information sheets No: 8 37720 issue 2. No: 9 & No: 10 35406 both issue 2 relating to the differences between UNF and ANF threads with a cross section of the thread profile. It also shows how to identify which are ANF and UNF nuts/threads. The sheets also refer to the use of BSF threads/nuts.
Phil

[Flywheel]

Thanks Phil.