Although we've been selling them for 40 years here at McFeely's™, we're amazed at number customers that are new to them. Trim heads are usually a #7 or #8 body with fine threads and a flat top head that is 30% smaller than a standard flathead. In trim work they are usually sunk beneath the surface and finished over with some type of filler. Like any fastener, they work best for intended application. Generally, we recommend using them in any application where a finish nail would be appropriate. Imagine having a small diameter screw that would let you actually pull a joint tight! Because of the smaller head, the #1 square drive is the preferred recess; a Phillips just would not work. The Spax T-Star drive system is also a good choice.
Trim heads are great running trim. In softwoods, they'll power right through the trim, drywall and into the stud. Hardwoods usually require pre-drilling to prevent splitting and ease the amount of torque required to set the screw. Softwoods should even be pre-drilled; if you don't, there is always a troublesome burr or chip on the edge that prevents your filler from binding. Finding the proper countersink for trim heads was always problematic because the proper size pilot was always in 3/8 in. diameter countersink, which was way too large for the screw. Other 1/4 in. countersinks only had pilots too small. We solved the problem: we worked with a US manufacturer to develop a specially designed heat treated 1/4 in. countersink with 1/8 in. pilot. This works well for all of our trim head screws. Generally, you'll just drill the first piece and let the screw do the work on the second piece.
Here's some important tips and a word of caution: you may never have a 100% success rate driving trim heads on a given job requiring many screws. Trim head's small head and recess just do not allow for much error. There is not much material to support the driver bit. All of our steel trim heads are heat treated steel but you can still break the head in high torque situations such as driving a 3 in. screw into an oak stair tread. The #1 recess is more sensitive to being driven off 90 degree axis. Once you get off center and start to spin, your best bet for success is to remove it (while you still can!) and try driving another. You may need to open up your pilot hole or lubricate with beeswax screw lube.
Besides trim, consider these screws for a few of these applications:
You'll find that 1-5/8 in. or 2-1/4 in. can secure the hardwood to the subfloor without making a huge, obvious hole. The smaller the hole, the easier it will be to hide. Match the color as close as you can (lighter is better than darker), and you can even draw in grain to break up the line.
Use special 3-1/2 in. and 4-1/2 in. screws to add jamb extensions for thicker walls. Drive right through the edge and if you're careful the reveal on your trim can cover the hole. No patching is better...right?
Trim heads can work great for attaching risers and tread to stair when used in conjunction with a good construction adhesive. They can also be used to toe-screw balusters in the right application. As with most fastener uses, check with your local code enforcement official.
Regular steel trim head screws usually have a fine thread and do not offer appropriate withdrawal resistance for decking. Smaller heads will pull through softer woods and composites. Ask yourself if you would put down your deck with a finish nail. Of course not! In most cases, with the exceptions noted below, trim heads are just not the best choice for decking.
Some harder composites and tropical hardwoods can use trim heads. In these cases you'll use a stainless trim head that will have deep wood tread like a standard decking screw. Care must be given because stainless is softer than hardened steel. Recesses are more prone to strip and the thin #7 or #8 may not have the torsional strength to be driven to the correct depth. Care must given to drill the correct pilot and or clearance hole. Kreg has a tool for that.
Match screw colors to your premium composite, PVC or encapsulated decking material with this guide. You will have a choice of 305 and 316 Stainless Steel or coated screws designed for outdoor use.
Straight through the jamb and shim and into the jack studs. With proper placement, they're easy to hide. Remember to use corrosion resistant screws such as our No-Co-Rode plated or stainless where needed.