Advice on Tapping Mishap

[brino]

Uggg. I fell right onto this trap even after reading this. Dementia sucks.

It happens to the best of us!

The reason I know that the problem exists is that I have been there.
I had taps that simply did not make sense, they did NOT match the diameter that they were marked.

I was hoping that writing it down somewhere would make me remember to double-check every tap that I pick up.....but I have gotten out of the habit.

Perhaps this refresher of the issue will make me remember......

Brian

 

[RJSakowski]

Given that this is in the UK, what is a possibility that the threads on either the tap or the casting are actually Whitworth threads. I haven't fully explored the ramifications but the 55º vs. 60º thread angle could create an issue. Do Whitworth taps cut true to form or do they come to a sharp vee?