I have a Heli-coil set but not the complete kit. What size do I need to tap a hole for a 1/4" thread heli-coil to screw in to? The set doesn't have all the info and I've never used 1 before.
Note the tap and drill are probably not common so I found a specialty business where I went to them directly in San Jose. There is 1/4 -20 and 1/4 - 28 both on the chart, but they use the same drill and tap, just the insert have different thread per inch course 20 or fine 28.