Thread of big end bolts and nuts?

[Derek 328]

Hi

I have a 3/8 BSF x 20 tap and die. This corresponds with the thread gauge on the stud.
BUT when I gently put either the tap (on the con rod) or the die (on the stud) it tightens and it is visibly shiny on the thread.

Can anyone shed any light as to why this is happening.

Why am I doing this? I have a con rod with a hole into the oil way just below the small end!!! I have sourced a con rod with no studs. Just want to move the studs from one to the other.

Furthermore, I need a set of new nuts, where can they be sourced, of the correct quality?

Thanks

Derek