Spehro Pefhany wrote:

On Tue, 02 Jul 2013 16:18:02 +0000, Safeman
wrote:

I need to source 90 of 9/16 UNC flush headed countersunk bolts/screws
overall length 2" and 10 of the same but overall length 2.5"

It doesn't matter what type of drive they have and preferrably threaded
the whole way, I could live with 1/2" unthreaded shank.
Any more than that I guess would be acceptable, just a lot of thread
cutting for me to do....

Anybody help, I have run out of ideas...

Neither Holo-Krome nor Unbrako lists 9/16" flat head socket. You may
be out of luck as far as a standard product goes.

Lots of options in hex head at McMaster, but no flathead. You could call
McM, they have a good reputation for locating odd stuff. I presume you
don't have the option of a more common thread size or perhaps
counterboring to fit a recessed hex head?