any tool to measure the size of both internal & external threads?
#2
Yes, it is called a Thread gauge and they are available at auto parts stores for a few bucks. OR, here are some free ones you can actually print off (both US and metric sizes).
http://www.boltdepot.com/fastener-in...read-Gauge.pdf
http://www.boltdepot.com/fastener-in...read-Gauge.pdf
http://www.boltdepot.com/fastener-in...read-Gauge.pdf
http://www.boltdepot.com/fastener-in...read-Gauge.pdf