I'm sure Twisted has the defintive answer for your problem. As a general note threaded devices are designed to be used at the square of the thread. That is if it is a 3/8-16 it should be threaded at least 3/8 into the material. I was told this by an Engineer many years ago and have always followed it. That's not to say that additional thread wouldn't exceed the strength of the threaded materal.
Larry
