On Wed, 25 Dec 2013 07:54:50 -0500, "dadiOH"
wrote:

"Stormin Mormon" wrote in message

I've been asked to anchor aluminum threshold
for commercial doors. About six inches wide, and
runs the width of two 36 inch steel doors. One
half of the threshold is loose, and needs maybe
four or so anchors.

Some how, I remember some blue anchors that look
a bit like drywall screws, but have really aggressive
threads. Anyone know what I need for the job?

Where to find these? Lowe's? Need flat head, so as
not to be a trip hazard. Can't have hex heads.

Tapcons (brand of concrete screw) come in blue or black AFAIK. IMO, either
is going to look crummy in a threshold; not only becuse of the color but
because the head will stick up slightly unless you are able to perfectly
countersink them, not always an easy task on thin aluminum.

Let me ask you, how was the threshold originally attached? I'd try to do it
the same way. One way that is common is to lay down a piece of PT, tapcon
it in and attach the threshold to it with smaller wood screws.
I've had pretty good luck on a few just blasting them full of low
expansion (window and door mounting) urethane spray foam. It sticks
like snot to anything and keeps the threshold from depressing/bouncing
as a bonus.. If mounting a new aluminum threshold to concrete, just
get urethane windsheild mounting compound and lay 2 beads on the
(clean and dry) concrete, and drop the threshold in place. It is there
"for the count".