Let me interject a moment. It is best to use a rethreader to clean threads and not a tap. Most of the broken taps that come to my truck are from rethreading. Most of those taps are broken with a sad story attached about getting the broken piece out. Thanks, tmm
http://www.mactools.com/shoponline/product/tabid/120/p-320457-48-pc-rethreading-kit.aspx
