Monday, February 1, 2010

GRK Fasteners

by Gaius Hennin, P.E.

Caution: The following blog was written by an engineer who likes to hear himself write. It is boring, wordy and overly technical. Before attempting to read, warn a family member about your whereabouts, as a deep slumber may spontaneously overtake you.

Those of you who have taken our design/build class have heard me describe the phenomenon of ‘cam-out’ in the Sheathing, Insulation and Fasteners class. Those of you who have driven a traditional 3” decking screw through 5/4 pressure treated decking have probably experienced it first hand. If you haven’t had the pleasure of experiencing it, let me explain. Cam-out is the very frustrating event where the torque provided by your drill exceeds the friction provided by your (usually Phillips) driver in your drill causing the driver to lift out of the screw head slightly and grind against the screw without turning the screw. Almost immediately, the screw and perhaps the driver become slightly damaged, making further progress even more difficult. If another cam-out incident occurs, damage to the screw can preclude even removal of the screw. As it turns out, the very shape of the Phillips driver was intended to allow, if not encourage, cam-out to happen to prevent the unskilled laborers on Henry Ford’s assembly lines from over-torquing screws.

About 18 years ago we were introduced to a screw manufacturer named GRK Fasteners™, whose line of screws utilizes a TORX™ bit (sometimes referred to as a star bit) instead of a Phillips bit. The beauty of the TORX™ driver is two-fold. First, unlike the tapered Phillips bit, the TORX bit is straight in profile so the resistance to turning provided by the screw does NOT tend to push the bit up and out of the screw head, resulting in cam-out. Second, the TORX™ bit has six flutes radiating out from the center of the bit compared to the Phillips bits’ four flutes, which increases the contact area and therefore the friction between the driver and the screw.

The use of a TORX™ driver is only the tip of the iceberg in terms of what sets GRK fasteners apart from most other screw manufacturers. GRK offers a complete line of fasteners from trim head screws to pre-painted screws to lag screws up to 20” in length. Everything about the screws says “Uber-grade” (their phrase). All GRK fasteners (except their PHEINOX line, which is stainless steel) are coated with a Climatek™ coating consisting of six layers of zinc and polymers. Climatek™ is an International Code Council recognized corrosion prevention coating (see ICC-NES Report NER-643) which allows the fasteners to be used with the new, highly corrosive pressure treated lumber. The screws have a patented detail at the tip which GRK calls their W-Cut™ Thread Design. This is a saw-like edge cut into the threads of the screw so that the screw slices through the wood as it is driven (like a circular saw blade), rather than pushing the wood to the side to create a space. This reduces required driving torque and virtually eliminates splitting which allows the screw to develop and maintain a high withdrawal strength. In addition the W-Cut™ Thread, the screws have a slice in the steel of the screw, perpendicular to the thread which makes the tip very sharp and allows for easy starts in even the driest and hardest woods. GRK calls this a Zip-Tip. The basic workhorse of the GRK screw line is the R4™ Multi Purpose screw, available in 59 sizes from 4x3/8” (#4 gauge 3/8” long) to 12x12” (#12 gauge 12” long). These screws, in addition to the features listed above, have a four threaded feature just above the regular thread of the screw, which slightly enlarges the hole in the wood as the screw is driven. This enlarged hole (after the threads) allows the unthreaded portion of the shank to pass easily through the wood, increasing the clamping force between the two pieces of wood being joined which increases the available shear strength of the screw. In short, it makes it much easier to draw two pieces of wood together tightly. Another nice feature of the R4™ is the self countersinking head, accomplished with six cutting edges on the underside of the head which, like the W-Cut™ Thread, actually slices the wood under the head rather than pushing it aside. This makes for a super clean countersink with no splinters sticking up around the head and no splitting. We use these screws for installing 2x6 and 3x6 decking on our timber frames, installing jamb extensions around windows and doors, building templates and deck framing (specifically using engineered lumber) where other screws just break. The R4™ is a pleasure to drive resulting in reduced installer fatigue. We have also noticed that our cordless drills can drive many more R4™ screws per charge than other types of screws due to reduced friction. Lastly, these screws lend themselves well to temporary applications like scaffolding and bracing due to high shear strengths and the fact that the TORX™ head does not wear out easily: these screws can be set and pulled dozens of times with no wearing or marring of the screw where the driver engages the screw.

GRK also has a line of screws designed for attaching to concrete. The Caliburn™ line of screws is available in ¼” through 19/64” in diameter and lengths from 1 ½” to 4 ¾”. These screws do not use a lead shield, so require only a small diameter hole to be drilled in the concrete. The hardened steel of the screw then cuts into the concrete as the screw is installed, resulting in ultimate withdrawal strengths as high as 5,724# per screw. We use these for installing sill plates into the vertical portions of a stepped foundation in lieu of j-bolts.

Several of the specialty fasteners offered by GRK include cabinet screws, composite decking screws, metal siding screws and Top Star™ Shim Screws. The cabinet screws, as the name implies, are intended for installing and constructing cabinets. The screws are quite thin to prevent splitting when attaching face frames to each other and have a built-in washer to distribute clamping forces over a greater area. This is very helpful when attaching cabinets to a wall where the screw is installed through the rear thin plywood of the cabinet. GRK’s composite decking screw has a self-countersinking head and rings under the head which trap the composite decking fiber to eliminate mushrooming of the fiber up around the head during installation. These screws also have the CEE thread feature which enlarges the hole in the decking, allowing the screw to easily pull the deck board tight to the framing. The Kameleon ™ line of composite decking screws comes in six colors to match most available decking brands. The metal siding screws combine all of the unique thread details of the GRK fastener with a built in washer (powder coated) and rubber washer to create a watertight fit between screw and siding or roofing. Lastly, the Top Star™ screw is incredible, though difficult to describe. It is intended for use installing doors and windows to allow the jamb to be moved in or out to level and straighten the jamb. This fastener consists of a screw within a screw. Using a specialty driver provided by GRK, the fastener is installed through a predrilled hole in the window/door jamb into the rough opening frame. Switching bits at this point allows the driver to engage a smaller screw within the fastener; turning this screw walks the window/door jamb in or out to get it perfectly level and straight. Without the Top Star™ this same procedure is typically accomplished through the use of shims and screws working against each other.

The last GRK I will discuss is my favorite, the RSS™ (Rugged Structural Screw). This screw is available in sizes from #10 x 1 ½” up to 3/8” x 16”. It has a built in washer, a CEE™ Thread, Climatek coating, a W-Cut™ thread, and hardened steel. With ultimate load capacities as high as 5,990# loaded in withdrawal and 2,065# loaded laterally, this is truly a structural screw. The thread on these screws is DEEP, which allows it to really bite into wood, more so than a traditional lag screw. The International Code Council has recognized the performance values of these screws (see ICC Report ER-5883) as equal to or greater than lag screws. Due to a thinner shank comprised of harder steel and deeper thread gullets, these screws can be driven with less torque than a lag screw without pre-drilling. Some of the RSS screw sizes are available in PHEINOX™ stainless steel, great for decks, docks and any other outdoor structures along our salty coast.

Why has it taken 18 years to write about GRK you ask? Well, we are finally stocking and selling them at our Woolwich, ME location. Please feel free to e-mail or call with any questions; chances are GRK has a high quality, easy driving, specialty fastener to make your project easier, and we have used it. As always, thanks for reading and remember-life is too short for bad screws.


  1. Great post, Gaius. Given the failure rate of a Phillips head screw, why are they sold at all any more? I shudder to think back on the hundreds of screws I've damaged and the hours of frustration. After reading this post, I don't think I'll use a Philips head screw again.

  2. Thanks Kevin-
    Phillips head screws still have a place and use-in gypsum wall board installation where the screws are only 1 1/4" long and require little torque. There are specialty drivers that can be used which have a large face that hits the gypsum surface and prevents the driver from advancing further; this causes the bit to cam out and prevent over-driving of the screws and tearing of the paper.

  3. These screws are not cheap! However they are great. I've used them and love them. Where do you guys buy yours? I get mine online at Let me know if you find them cheaper somewhere else.