GRK 16083#8 x 3-1/8" RT Composite Exterior Trim Screws 514 Count

Why these GRK trim screws ended up in my everyday kit

I keep a few types of fasteners in my bags at all times, and GRK’s RT composite trim screws have earned a permanent spot. They’re #8 by 3-1/8 inches, with a small trim head and an underhead reverse thread that’s designed to reduce mushrooming in composite and cellular PVC. In practice, that combination hits a sweet spot for clean, low-profile fastening on exterior trim, decking, and PVC profiles—without the visual baggage you get from a typical bugle head.

I’ve used them across a handful of jobs: face-fastening composite decking boards, hanging PVC fascia and skirt boards, attaching thin composite cladding accents, and even in a couple of interior trim fixes where a compact head mattered. They’ve been reliable outdoors through freeze-thaw cycles, rain, and summer heat, and they’ve remained easy to back out when I needed to pull a board or make a repair later.

Design and what it gets you

• Trim head: The small diameter head is the star. It sits quietly on the surface without the crater a bigger bugle head leaves, and the hole is easy to disguise with filler if you’re going for a near-invisible look.
• Underhead reverse thread: On composites and cellular PVC, mushrooming is a fact of life, but the reverse thread under the head genuinely helps. It compresses and cuts the top fibers as the head seats, leaving a flatter result than standard deck screws.
• Torx drive (T10): A precise recess that resists cam-out—when paired with a good bit and proper technique.
• Exterior-ready coating: I’ve seen no rust streaks or red bleed-through around fastener heads after seasons outside, and the recesses have stayed clean enough to accept a bit for removal.

The 3-1/8-inch length is ideal for face-screwing 5/4 decking into joists with enough bite, and it gives you comfortable margin anchoring 3/4-inch or 1-inch PVC trim into framing without bottoming out.

Driving experience: the good, the bad, and the fixable

When driven correctly, these sink beautifully. You get predictable pull-down and a neat finish, even in less forgiving composite boards. The reverse thread does most of the finishing work; I rarely need to follow with a countersink.

That said, a few notes will save you headaches:

• Use a high-quality T10 bit—preferably a hardened one—from a reputable brand. The included bit is serviceable but wore quickly for me. With a worn bit, the small T10 recess strips more easily.
• Back off the impact. You don’t need monster torque here. I prefer a drill/driver with a clutch or an impact set to a low speed, letting the screw cut rather than letting the tool hammer it home.
• Keep alignment true. A slight angle plus high torque is the fastest route to a stripped recess.
• Pre-drill near edges or in brittle stock. On dense hardwoods or close to ends in cellular PVC, a quick pilot and a countersink pass keeps everything tidy.

If you do strip a recess, removal gets tricky; a sharp T10 and steady pressure often rescues it. Worst case, a pair of locking pliers on the trim head will turn it out, but that defeats the purpose of a clean finish. Again—use a better bit from the start and this becomes a rare event.

Performance in composite and PVC

This is the fastener I reach for on cellular PVC trim boards, window surrounds, and skirt boards. The small head virtually disappears, and the reverse thread minimizes the telltale pucker around the head. On some composites, you’ll still see a whisper of mushrooming—that’s the nature of the material—but it’s subtle and easy to tame. Two approaches I use:

• Pause as the head starts to seat, let the reverse thread do its work, then give a final, gentle bump.
• For a near-invisible finish, tap the slight ridge back flush with a nylon mallet and fill the tiny recess with matching PVC or exterior-grade filler. The small head makes the fill tiny and unobtrusive.

Pull-down power is excellent. The upper counter-thread helps pull the board tight to substrate in that last half-inch of travel, which is exactly what you want when you’re straightening a slightly crowned deck board or flattening a PVC fascia that wants to move.

Wood applications

Despite the “composite” label, these are perfectly at home in wood. I’ve used them with cedar, pressure-treated pine, and red oak. In pine, they drive without splitting in most situations; in harder or brittle species, a pilot hole keeps things civilized. For subfloor squeaks or tongue fastening in hardwood flooring repairs, the trim head tucks away cleanly and holds firm—just be sure you’re not relying on them for structural connections; they’re trim screws, not ledger or structural deck screws.

Durability and removal

Long-term, they’ve been kind to the materials they hold. I haven’t seen rust staining on composite or PVC, and the recess does not pack with corrosion, so I can re-seat a bit years later to back them out. On decks where I’ve needed to pull a board for a hidden wire run or replace a damaged plank, these have been cooperative. That alone makes them worth keeping on hand.

Limitations and compatibility

• Not for hidden-fastener jigs. These are not a substitute for specialty screws used in side-angle jig systems. The head geometry and threading are built for face-fastening; forcing them into a hidden-fastener workflow can jam tools and damage boards.
• Bit size and recess: The T10 is small. It’s fine when you use a fresh, high-quality bit and correct technique; it’s unforgiving when you don’t.
• Not structural: I wouldn’t use these where code calls for structural screws or where shear loads are significant.

Value

They aren’t the cheapest box on the shelf, but they undercut many proprietary composite deck screws and hidden-fastener systems while delivering a cleaner look than standard bugle heads. The time saved on pre-countersinking and the tidy results on PVC and composite make the cost easy to justify on trim and face-fastened deck work. If you plan to use them for a large project, figure a few extra bucks in your budget for quality T10 bits—you’ll come out ahead in time and frustration.

Tips for best results

• Use a premium T10 bit; replace it at the first sign of wear.
• Run your driver slower than you think you need; let the threads cut.
• Pre-drill near ends, in dense hardwood, or wherever splitting is a risk.
• For ultra-clean finishes on PVC/composite, stop just shy of fully seated, then finish with a gentle trigger bump. Tap any slight mushroom flat and fill if needed.
• Store the screws in a sturdier container if they’ll live in a truck; the factory tubs can pop open when abused.

Who these are for

• Deck builders and remodelers who face-fastening composite or wood boards and want a discreet head with strong pull-down.
• Trim carpenters working with cellular PVC and composite trim where a tiny, clean head and reduced mushrooming make all the difference.
• DIYers upgrading exterior trim who want professional-looking results without switching to specialized systems.

If your work leans more toward structural framing or hidden-fastener decking, look elsewhere. These shine in the trim and finishing lane.

The bottom line

GRK’s RT composite trim screws are a dependable, tidy solution for exterior trim, cellular PVC, and face-fastened decking. The small trim head keeps the look clean, the underhead reverse thread genuinely reduces mushrooming, and the coating stands up outside. Their one Achilles’ heel is the small T10 recess: use a hardened, high-quality bit and moderate driving force, and they reward you with smooth driving and easy removal down the road.

Recommendation: I recommend these screws for anyone fastening composite or PVC trim and for pros or DIYers who prefer the simplicity and control of face-fastening decking. They deliver a clean finish, strong pull-down, and long-term serviceability. Just bring good Torx bits and reasonable technique, and they’ll make your work look better with fewer steps.