I checked the screws I used for the stair landing. There were the TORX screws, which had “coated for exterior use” finish and “Suitable for pressure treated lumber”. The TORX screws had a small star bit included that fit snuggly. The yellow coded bits I had were too small, and the red coded were a “fit” but significantly looser than the supplied bit.
The Deckmate screws used a larger (coded green) bit. The larger bit seemed to do a better job, but perhaps the paint-like finish provided some lubricity. They seemed to driver easier.
My bigger knock against the TORX was the applied finish. Labeled “coated for exterior use” and “suitable for use with pressure treated lumber”. The finish, which was a dull gray, appears to be impact plated with zinc. If the same process is used in thicker coating it would qualify for “cold galvanizing”.
Impact plating and cold galvanizing offer significant attractions for manufacturers. The process includes pre-cleaning the parts to be coated, and then putting the parts along with small zinc pellets in a tumbling barrel. The parts are then tumbled and the zinc sticks to the parts much like cooked spaghetti sticks to the wall. It is a strictly mechanical bond. The big advantage to manufacturers is that it does not require all the EPA compliance equipment (which can cost over a million dollars) that zinc plating needs, nor the high energy costs that hot-dipped galvanizing requires.
On the minus side, the strictly mechanical bond is not so strong. On cold galvanized nails, the zinc on the face of the nail is usually flaked off with the first strike of the hammer. I did not see any flaking on the screws. Of course I did not really inspect the interior of the star socket, nor the condition of the threads after driving.
Neither manufacturer called out the actual finish. Which alerts my sneaky-marketing-department-antennae.
Of the two coatings, I would prefer the organic (painted) coating. Most of those finishes bond at the molecular level and have better adhesion than impact plating.
As an aside, never use cold galvanized nails. They are not the equal of hot dipped galvanized.
And very heavy coating of electro-zinc plating also tend to have flaking issue.
Most fasteners we see with zinc plating have “commercial zinc”, which is “nominal 0.0003” thick, called out as “three tenths of a thousandth” or just “three tenths” thick.
The nominal” part means that they are plating until the entire part has zinc coating, which means much of the part is at 0.0003”, but the hard to reach parts may have significantly less.
There are specs (mostly military) that call out “0.0003” minimum” or “0.0005” minimum”, but you will not likely come across this with commercially available hardware.
