Self-drilling screws, often called "Tek-screws" can be immensely helpful for making strong joints on the fly. These are designed to be the pinnacle of efficiency, but the reality on the job site is frequently one of immense frustration. Workers contend with screws that kick off their bits, screw points that burn out and refuse to drill, heads that snap off upon seating, and threads that strip in thin metal. 

This comprehensive resource identifies the root causes of these failures, which are rarely due to "bad screws" and almost always due to misaligned physics: specifically, the incorrect Applied Force (drilling force), Material Thickness, and RPM.

Quick Answers for the Frustrated Installer:

Screws Threads Are Stripping Out:

Inevitably, stripped screws were overtightened. An impact driver is not a good choice for fastening into metal, especially thin metal. Use a drill/driver with the clutch set low so it stops spinning when the screw is seated. Slow down and monitor carefully. 

Screws Aren't Drilling:

There are multiple issues that can cause screws to not drill.

-Most commonly users are not applying enough force. Ideally 40lbs+ applied directly inline with the drill/bit is what will make steady progress, and more is better. That is surprisingly difficult to apply depending on where the joint is relative to your body. Try to position yourself more closely to the joint, and use your free hand to stabilize yourself on the material you're drilling into and to oppose the force you need for drilling. 

-If you're using an impact driver at full speed, slow down the rotation and/or switch to a drill. Impacts can run up to 3500 RPM+, but slower like 750-1000 RPM is much better. Most modern drills and impacts have variable speed triggers, so just backing off can help. 

-Add up the stack thickness: self drilling screws are not designed to fasten a stack thicker than what their drill tips can auger the material out of. If the drill flutes are buried while drilling, the screw will fail. For example, the most common Tek3 drill tips can only work with a maximum of ~1/4" (6mm) total. A 1/8" bracket fastened to a 1/8" base material (1/4" total) pushing the limit. In contrast a screw with a Tek5 tip can handle 1/2" (12.5mm). 

Screws Are Kicking Off Bits:

-Our Autolock drivers were made exactly for this purpose and work great as long as you have sufficient access around the screw for the larger diameter of the tool. 

-Make sure you're applying force directly inline with the bit. An unbalanced load (side load) on the bit or screw tip is what causes this. 

-If you're using a magnetic driving bit, make sure you don't have excess of drill shavings stuck to the magnet. This prevents proper engagement between the bit and the screw, specifically preventing the face of the driver from pushing on the flange/washer which keeps the screw and bit aligned. Use a needle nose pliers, tweezers, or something sticky like a ball of mastic, duct tape or gum to remove metal shavings.

There are also cleanable reversible bits by Malco, Dewalt, and Milwaukee, which make that far easier and often have 2 common sizes on one bit. These are popular so they are available at many local hardware stores.

Screw Heads Are Breaking Off

-Most often, using an impact driver is the root cause of this issue. Simply put, they can apply way too much impact energy to a screw like this going into a joint with little give. If you must use an impact, use only a partial trigger pull and slow down when the screw is close to being fully driven. Do not use extra trigger pulses to tighten the joint without careful monitoring. All too often this process seems simpler to manage to many people than it really is, so applying caution is key. A clutched drill/driver is a better choice. 

-If you're using a drill, make sure you're either using an appropriate clutch mode, or slow down the drill before the screw fully tightens to limit the risk of over-torquing the screw. In delicate cases you may even consider fully seating screws with a manual ratchet wrench and socket. 

-In some cases, if the screw threads start to engage the top layer being fastened before the screw has fully drilled through the base material, the screw will jack that top layer away from the base material. The screw can then tighten into the top layer, where further attempts to tighten could shear off the screw head. Ideally, get a screw with a longer drilling tip, pre-drill the hole with a traditional drill bit, or drill a clearance hole in the top material being fastened which is larger than the screw diameter.  

A deeper dive into these factors:

• Drilling Force-screws will simply not drill without enough:
  • Super Common: From working with and talking to hundreds of installers over the past 15 years, this is the #1 root cause of issues where people can't get self drilling screws to drill. 
  • How Much: As a rule of thumb, you want 40lbs or more down force on the screw to drill into the base material. This is very different than any sort of wood screw which will start to penetrate a wood surface and draw itself in often with very limited 5-10 lbs of force. 
  • Position/Reach makes a huge difference: Applying 40lbs of force to a drill for is easy to do when drilling straight down on a workbench. You can safely and easily push with your body weight. This becomes much more challenging when driving in other positions. Applying 40 lbs of force when drilling horizontally isn't too bad if you're fastening within about 1 foot of your shoulder height and within 1 foot of your shoulder from side to side. When you're reaching further above, below, or to the side of your body, the amount of force you can apply and the amount of time you can apply it for quickly decreases. This means the ability to drive screws greatly decreases. 

• Drilling Capacity (thickness of materials)

  • The Tek Point Numbering System:
    The "Tek" number refers to the length of the drill flute and, consequently, the thickness of steel it can penetrate.

    Point Length	Max Material Capacity	Typical Application
    Tek 1	0.080" (2.0mm)	Thin sheet metal, HVAC ductwork
    Tek 2	0.140" (3.5mm)	Metal lath to studs, light framing clips
    Tek 3	0.210" (5.0mm)	The standard "general purpose" screw
    Tek 4	0.250" (6.5mm)	Heavy framing, thicker structural clips
    Tek 5	0.500" (12.7mm)	I-beams & thick plate, multiple layers

     

  • Critical Insight: "Capacity" refers to the total thickness of all layers being joined. If you are attaching a 2mm bracket to a 10mm steel column, the total thickness is 12mm. A Tek 3 screw (max 5mm) will fail. The flutes will disappear inside the steel before the tip drills all the way through, causing chip impaction and eventually burnout. Solution: You must use a Tek 5 screw for this application, even though the bracket is thin.

• The Great Debate: Impact Driver vs. Drill/Driver
  
  • We love impact drivers, but there are a number of often unintuitive reasons why they're not appropriate for fastening with self drilling screws. 
  • The Mechanics of the Impact Driver
    • An impact driver relies on a rotational hammer-and-anvil mechanism. When resistance is met, it delivers rapid, high-torque concussive blows (impacts) to rotate the fastener.
      
    • Pros: High torque, minimal reaction torque (saves the operator's wrist), compact size.
      
    • Cons for Tek Screws:
      
      • Fracture Risk: The hardened tip of a Tek screw is brittle. The high-frequency hammering of an impact driver can shatter the cutting edges of the drill point before it finishes cutting, leading to failure
      • Lack of Control: Impact drivers generally lack a mechanical clutch. When the screw seats (the head hits the metal), the tool continues to deliver massive torque spikes (up to 2000 in-lbs or more). This instantaneous load often exceeds the shear strength of the screw head (snapping it off) or the shear strength of the threads in thin metal (stripping the hole).
      • Speed and fluctuation: Many impact drivers at full trigger pull spin much faster than what is ideal for tek screws. Also, impact drivers go from high RPM spinning to impacting cycles based on load. If an impact driver starts hammering prematurely that can slow the rotation down to ineffective levels for drilling, and is going to be slower tightening the fastener after the drilling is complete.
  • The Superiority of the Drill-Driver
    • For professional self-drilling screw installation, specifically in structural steel, a high-quality drill or a dedicated screw gun is superior. 
      
      • Pros:
        
        • Relatively lower RPM: allows the operator to maintain a more optimal speed for the steel thickness, preventing burnout.
          
        • Clutch Control: The adjustable clutch allows the operator to set the tool to stop spinning exactly when the screw is seated. This prevents stripped threads and snapped heads, ensuring a uniform compression of a sealing washer, when present. 
          
        • Simple, consistent rotation: Drills apply smooth, continuous rotation, which is best for drilling. It will also seat the screw more quickly. 
  • The Verdict
    
    • Use a Drill/Driver (with Clutch): For precise work, sealing washers, thin sheet metal (to prevent stripping), and heavy structural steel (to prevent tip fracture and maintain optimal RPM).
    • Use an Impact Driver: Only acceptable for wood-to-metal connections or medium-gauge framing where speed is prioritized over precision, and where the operator is highly skilled at "feathering" the trigger to avoid over-torquing. Note: Even then, many manufacturers void warranties if impact drivers are used.
      

A few more tricks

• The Pilot Hole Compromise
  • Ideally, self-drilling screws do not need pilot holes. However, in some cases such as extremely hard steel or when working near or beyond the maximum drilling capacity of a screw—a pilot hole can save the day.
    
  • Use a standard drill bit to pre-drill the hole. Consult the chart below for the specific screw size 
    
  • Benefit: This removes the burden of drilling from the screw, leaving it only the job of tapping and clamping.

  • Recommended pre-drill bit sizes:

    Screw Size	Recommended Drill Bit Size
    #8	#29 (0.136")
    #10	#21 (0.159")
    #12	#13 or 3/16" (0.187")
    #14 (1/4")	#1 or 7/32" (0.228")

    **Note, the bit size should be equal to or smaller than the hole the screw tip would drill to prevent screws from stripping out too easily. Always drill a test hole to verify before drilling many. 

• Clearance Holes:
  • When fastening two pieces together, a larger hole in the top piece will prevent screw jacking, allow better removal of drill shavings, and allow the two materials to be better clamped together.
  • This can be particularly important for example if fastening a thick wood board to a steel surface.  This allows the screw to only thread into the steel, not the wood.
  • Special wing-tipped screws are made for drilling an appropriate clearance hole in wood when fastening into steel. The wings are designed to break off when screw starts to thread into the steel. 

Do you have any insight we should consider to further expand or improve this article? We'd love to hear it-please reach out!