Drill Capacity: The benefits of self-drilling screws

Today, there is a better selection of fasteners for metal building construction as compared to just a few years ago. With the variety of fasteners on the market, it should be the responsibility of the supplier to educate the contractor on which fasteners to use on a specific application.

Self-drilling screws, such as the DF brand screws, are used for stitching and sheet-to structural applications. The fasteners have taller, stout hex heads which create better engagement with the socket facilitating a more efficient drilling operation. To determine the correct self-drilling point, the contractor must first identify the total thickness of material being fastened. The length of the drill bit on the fastener will determine the drilling capacity of the screw.

For instance, a T-1 is used for sheet-to-sheet stitching with a total steel thickness of 0.024- to 0.095-inch (0.6- to 2-mm). T-3, or purlin screw, is used for a total steel thickness of 0.036- to 0.21-inch (1- to 5-mm). T-4s are used for a drilling capacity of 0.125- to 0.375- inch (3- to 10-mm). T-5s have a drilling capacity of 1/4- to 1/2-inch (6- to 13-mm).

Recently, Kansas City, Mo.-based Dynamic Fastener introduced the Fenderhead #14 diameter stout T-5 with 5/8-inch (16-mm) drill capacity. The giant washer face measures 5/8-inch outside diameter and provides superior pull over values and creates more than 100 percent additional bearing area as compared to the common 7/16-inch (11-mm) outside diameter washer face.

Due to the 5/8-inch washer face, some contractors have used this screw for decking in lieu of burning 5/8-inch puddle welds. This eliminates the hassle of repairing weld burn-throughs.

When installing self-drilling screws, it is critical to use the proper screwgun. A 2,500 rpm screwgun is required for T-1 and T-3’s. A 1,000 rpm screwgun is recommended for T-4 and T-5 screws. When drilling through 1/4-inch or thicker steel it is very important to use a slow rpm/high torque screwgun. A Dewalt 269 with 1,000 rpm’s is a perfect example of a suitable tool. If you use the very common 2,500 rpm screwgun (DW 268) or 2,000 rpm screwgun (DW267) to drill into 1/4-inch or thicker steel, then you will prematurely burn up the motor in the screwgun. Plus, you will burn up the points of your screws at an unacceptably high rate. Everyone knows that there is a direct tradeoff between high speed and high torque. When drilling thick steel, high torque is what you need.

Self-drilling screws are available in #6 – 5/16-inch (8-mm) diameter, from 1/2- to 8-inch (203-mm) long, with or without a sealing washer. They are available with a hex, Phillips and Torx head. The low profile head is excellent for standing-seam clips or architectural clips to steel. DF brand selfdrilling screws are available in stainless steel, zinc and our Dyna-Coat 1,000-hour salt spray premium coating. It is designed to provide excellent corrosion resistance for metal fasteners. Fasteners that are coated with Dyna-Coat exhibit excellent resistance to marring, chipping and abrasion. The color of the coated fastener is Metallic Silver.

Our coating process insures that the fasteners will not have any hydrogen embrittlement. Dyna-Coat employs several forms of corrosion resistance, such as replacement, inhibition, envelopment and electrochemistry. These coated fasteners also have strong resistance against acid and alkaline chemicals. Dyna-Coat also passes the 1,000-hour salt spray test.

Self-Tapping fasteners are recognized in the metal building industry as Type A, B or AB. The Type ‘A’ fasteners, which have a coarse thread and a sharp point, are commonly used as side over lap (stitch) fasteners and flashing fasteners for metal cladding. They are also used as structural fasteners to attach cladding to subgirt framing whose thickness is 18-gauge or lighter steel, or into wood. The ‘B’ fasteners, which have a fine thread and a blunt point, are used primarily to secure cladding to heavier building structural members whose steel thickness is 16-gauge to 1/2-inch. The Type ‘AB’ fastener has a similar thread as the Type B screw, but its point angle is the same as the Type A.

All three tapping screws require a predrilled hole before installation, unless going into very thin or soft materials. Panel and structural thickness will determine the correct drill bit. Our salespeople at Dynamic Fastener can provide the correct hole size based on fastener requirements.

Self Tapping screws are stocked in a #14 diameter, from 3/4-inch (19-mm) to 8-inch long, with or without a sealing washer. They are available in carbon steel and 300 series stainless steel. Type-17 points are also known as a “wood self-driller” because they drill into wood so much quicker as compared to a type ‘A’ pointed screw.

Type-17 fasteners are available in #8 to #14 diameter, from 1/2- to 6-inch (152-mm) long. They are available in Zinc or with the Dyna-Coat 1,000-hour salt spray premium coating or 300 series stainless steel.

Ken Webb has been involved in the metal construction industry for the past 22 years with Dynamic Fastener, Kansas City, Mo. More information can be found at