Peter,
What you need is a bottoming tap. Or, you could take a regular fluted spiral tap and grind off the lead in tapered section of the tap. Sometimes I actually prefer this method, especially with very short threads like this braze on, because even a bottoming tap will have a slight lead in. If you decide to grind a tap down, make sure you deburr it before use. Test the tap in the appropriate sized nut to make sure it spins free without catching or binding. Also, be careful to not cross thread or strip out the braze on. There aren't that many threads to begin with. Use a cutting oil.
Jay Sexton Sebastopol, CA
CR, The right downtube shifter braze-on on my 1953 Claud Butler New Allrounder needs to be tapped out. A Cyclo Benelux shift lever screw or damper (tried three of them) can only thread approx half way down until it hits damaged threads. I'm making do with some washers to keep the damper in the good threads, but I want to fix it.Please advise on tapping this brazeon out regarding thread specification and other matters (I assume a blind tap is used, but I'm not an expert).
Thank you for any advice, Peter
Peter Brueggeman
San Diego California USA
pbrueggeman(AT)ucsd.edu