Re: bolts with square threads

[Nolan Penney <npenney@erols.com>]

>My 70 TR6 has bolts that have square threads (3 sides have contact
>surface) that are used to hold body panels together and also to bolt 
>the doors to the hinges, hood & trunk lid to the hinges, etc.  

They are acme threads.  Common in industrial applications, such as the 
scissor jacks for cars.  Find an industrial supply store in your area 
and ask them about it.  They'll have what you need, or steer you right.