Self-tapping screws form threads in an existing hole. Self-drilling screws drill that hole themselves, then form the threads, all in one pass. Every self-drilling screw is also self-tapping, but most self-tapping screws cannot drill. That single difference decides whether you need a pilot hole, how fast you install, and how much steel the screw can handle.
Picture a roofing crew with a box of self-tapping screws and a run of steel purlins with no pilot holes. And a length of steel purlins with no pilot holes; the screws slide around, the drill fails to operate, and the schedule is delayed. The screws weren't defective; they were the wrong type for the task.
This guide gives a comprehensive overview of self-tapping self-drilling screws, from A to Z, and sets out a side-by-side explanation of self-tapping screws and self-drilling screws, covering how each type works, their drill points, the materials they can be used with, the different sizes available, the coatings offered, the process of installation, and how to choose the correct type before placing an order. Both sit within the wider industrial fasteners range at Wootz.work.
What makes the difference important?
Those who look for self-tapping self-drilling screws are generally aiming to avoid one of three expensive errors.
The first situation involves an installation that has come to a standstill. Since self-tapping screws require a hole to be pre-made in metal, those teams who expect the screws to drill into the metal end up wasting time and wearing out their drill bits.
The second is paying for a capability that you never use; self-drilling screws are more expensive per piece, whereas if the panels arrive with pre-made holes, self-tapping screws can be used to achieve the same result at a lower cost. The third is a joint that fails late; a drill point that is too short or a coating that is too thin might pass the first inspection but still fail when on site.
What is the difference between self-tapping and self-drilling screws?
The difference is the tip: a self-tapping screw has a pointed or blunt tip that cuts or forms threads inside a hole, while a self-drilling screw has a drill-shaped tip that first makes the hole. For a quick comparison of self-tapping and self-drilling screws, see below.
A single point regarding nomenclature helps to avoid confusion: although 'tek' began as a brand name, it is now used as a nickname for self-drilling screws in general.
People frequently inquire if the two types can be used interchangeably. The answer depends on the application. Self-drilling screws can generally perform the tapping function, but using them where self-tapping screws are sufficient may cost more than necessary. Self-tapping screws, however, may not be suitable where the screw must drill through multiple or thicker steel layers.
What are self-tapping screws?
Self-tapping screws form their own matching thread as they are turned. They do not drill the hole. With metals, it is necessary to first drill or punch a pilot hole.
There are two ways a screw taps its thread:
- Thread-forming: In the case of thread forming, the screw bends the material out of the way without taking it away; this is suitable for use with plastics and thin sheet metal.
- Thread-cutting: For thread cutting, the screw has cutting edges, usually with a flute that has been machined into the thread, and it removes material as it progresses, a feature that is appropriate for harder or more brittle materials.
When selecting thread-forming self-tapping screws, the difference is important since threading in this case produces no chips and results in a tight fit in soft materials; that is the reason why thread-forming self-tapping screws are most used in plastics. On the other hand, cutting requires less driving force in hard materials but leaves behind swarf that has to be cleared.
The shape of the tip contributes an extra aspect to the matter. Types A and AB have a pointed end, while types B and F have a blunt tip. The sharp point can be started easily in thin sheet metal, whereas the blunt tip is suitable for use with a pre-drilled hole.
In the case of inch-series drawings, tapping screws are governed by the ASME B18.6.3 standard issued by the American Society of Mechanical Engineers. According to the American National Standards Institute's summary of the 2024 edition, the standard includes machine screws, tapping screws and metallic drive screws; older drawings might still refer to B18.6.4, which has been incorporated into B18.6.3.
Next to these are the bolts and screws which make up the wider family of industrial fasteners as listed by Wootz.work.
Self-tapping screws for sheet metal
Self-tapping screws for sheet metal are used widely in enclosures, brackets, ducting and appliance panels. The pilot hole is generally punched or drilled during the same fabrication operation as the component, thus enabling a quick assembly without having to pay for a drill point.
There are two checks to ensure that sheet joints are tight: match the pilot hole to the thickness of the material and make sure the screw is square with the panel. If the hole is only slightly larger than necessary, it will strip thin sheet, and if it is too small, it may crack the material or cause the screw to snap.
Where self-tapping screws struggle
Self-tapping screws have difficulty when there is no pre-drilled hole and when the steel is thicker than thin sheet; moreover, they struggle with very brittle materials since forming might cause the wall to crack. Cutting screws perform better in brittle materials, but they produce chips which have to be removed from the joint.
What are self-drilling screws?
What do self-drilling screws actually look like? Self-drilling screws have a drill bit tip at the end of a threaded shank; this tip drills the hole, and the threads then engage the wall of that hole. A single operation carries out drilling, tapping, and fastening.
The number indicated is the tip number, and the higher the number, the longer the drill point and the greater the steel thickness rating. The SAE International J78 standard includes the dimensional and performance requirements for carbon steel self-drilling tapping screws for point types 2, 3, 4, and 5; the page for this standard can be found on the SAE International standards website.
A #5 point is generally given a rating for steel about half an inch thick in total; the ratings for the smaller points differ according to the manufacturer. Refer to the data sheet and compare it with the J78 tables.
Three rules keep the drill point alive:
- Count the whole stack, every steel layer plus any gap between them.
- Don't choose a point that's too short: the threads engage before the hole is through and the screw binds or snaps.
- Don't choose a point that's too long for thin sheet: the sheet tears and the point loses its grip.
Self-drilling screws for metal
Self-drilling screws used for fastening metal are the usual choice in roofing, cladding, steel framing and ductwork; they are used for joining metal to metal and, using the appropriate tip, also for joining timber to metal. The section on the construction industry explains the role of this type of fastening in building work.
People generally call them tek screws, so if a supplier hears that term, they will still request the point number, the gauge, the head style, and the coating. When you place an order for self-drilling screws intended for use in metal, provide all four of these details, and there will be no need to guess. You should ask for the same information when ordering tek screws for metal from any supplier.
Where self-drilling screws struggle
Self-drilling screws have difficulty when the stack is thicker than the point rating, when the steel is hardened, and when the base metal is stainless; they also lose their edge if the driver goes too fast, and the point becomes dull from the heat before the hole is completed.
Self-tapping vs self-drilling screws: which one fits which job?
When choosing between self-tapping and self-drilling screws, you should select the type that matches what is already present in the joint. In the case where a hole has already been made, self-tapping screws are sufficient; but if no hole exists and the steel is thick, self-drilling screws are the better choice.
Self-drilling screws are more expensive on a per-piece basis, although they do save labor and drill bits. Self-tapping screws are cheaper but require one additional step. When comparing self-tapping and self-drilling screws, price is only one factor to consider, and neither should be regarded as the default option; you should count the number of holes you have.
Which materials work with each screw type?
The base material comes after the holes and is the second major filter.
In practice, there are two points to note. Firstly, self-tapping screws are widely used in enclosures, brackets and appliance casings, while pan-head tapping screws are frequently found in the metal cases of electrical equipment. Secondly, self-drilling screws are available for use in stainless steel, but it is more difficult to drill into stainless steel than into mild steel. You should check with your supplier both the material in question and the rated substrate.
It is worth mentioning that self-drilling screws for use in wood and metal have a particular recommendation. People frequently ask which type they should select, and in this case the ones with wings are the best. The wings cut out a clearance hole in the wood, and when they come into contact with the steel, they break off so that the threads can bite into it. Without wings, the threads grasp the wood and hold the boards apart.
When teams decide on steel grades before selecting fasteners, the page on material expertise explains how Wootz.work handles material selection. The sheet parts that are to receive these screws are provided by the sheet metal fabrication service.
How should a buyer choose the correct screw? A checklist
Before you prepare your specification for self-tapping, self-drilling screws, go through the six questions.
- Is there already a hole in each layer?
- What is the total amount of steel thickness, taking into account any gaps?
- What is the material in question: mild steel, stainless steel, aluminum, wood, or plastic?
- Will the joint be situated outdoors in a salty environment or in a washdown area?
- Which driver will the crew choose, and will a washer seal be required?
- What is the volume, and is the driving time more important than the piece price?
In the case of thin sheets with holes, self-tapping screws for sheet metal are generally sufficient. If you answer those six questions, then the appropriate choice will become clear. Since holes are present, the material is thin, and the volume is low: use self-tapping screws. When there are no holes and the material is steel, ranging from light gauge up to thick plate, with a high volume: use self-drilling screws. Mixed requirements are common, and so a single project may include both self-tapping screws and self-drilling screws in different joints.
What varieties, types and drives are available?
A screw gauge is a number, not a drill point; it determines the diameter, whereas the drill point number determines the steel capacity. Since they are independent, a #12 screw can take any point number that the manufacturer offers.
Heavier roofing and cladding typically use #12 or #14 screws; lighter ductwork and thin framing use smaller gauges. You should refer to the catalog since thread forms and head styles are not the same in all product lines.
Head style follows the job:
- The hex washer head is the most commonly used type for roofing since the built-in washer provides a wide bearing surface and secure driving.
- The pan head has a low profile and is commonly found in enclosures.
- When the head is flat or countersunk, it makes contact with the surface.
- The wafer type has a very low profile, which is suitable for concealed mounting.
The way in which screws are driven is just as important as the type of head they have, whether these are self-tapping screws or self-drilling screws; hex drives are suitable for use with impact drivers, and Phillips and square drives are generally used for lighter tasks.
What coating should self-tapping and self-drilling screws have?
The type of coating determines how long both self-tapping screws and self-drilling screws last when used outdoors; the base metal determines the strength, and the coating determines the corrosion resistance.
When you are buying either self-tapping screws or self-drilling screws, ask for two kinds of proof regarding outdoor use. The first kind is the salt spray hours as specified by ISO 9227, which is the International Organization for Standardization; this is a test method, not a guarantee of how long the product will last in the field. The second kind is the coating thickness measured per lot.
There is one further question regarding hardened self-drilling screws. Since hardened steel can be prone to hydrogen embrittlement after electroplating, this aspect is evaluated according to a separate standard for hydrogen embrittlement testing and not within SAE J78 itself. Find out how your supplier deals with it.
A case study involving the use of Magni coating and heat treatment on solar-grade bolts and nuts has already been published. When considering the different rust-prevention coatings, the guide comparing seven of them is helpful.
The fastener services offered by Wootz.work include testing for salt spray and coating thickness, and the quality assurance page describes how inspection and traceability function.
How do you install these screws correctly?
Even well-made self-tapping screws and self-drilling screws fail if they are not installed properly. Carry out the steps in this order.
- Check the total thickness and the point number.
- When using self-tapping screws in metal, it is necessary to drill a pilot hole that is only slightly smaller than the diameter of the screw.
- Keep the driver directed straight at the surface.
- Drive it at a low speed using steady pressure, since high speed causes the drill point to heat up and become dull.
- Stop when the washer seats. Do not overrun.
The size of the pilot hole is important in both directions when using self-tapping screws; if the hole is too big, the thread will be loose, while if it is too small, the screw may break or the material might crack. You should use the size given on the manufacturer's data sheet.
Common mistakes:
- Using a self-tapping screw in steel with no pilot hole
- Choosing a point that is too short for the stack
- Forgetting to count gaps between layers
- Driving too fast and burning the point
- Overdriving and cupping the washer, which leaks
- Using zinc-plated screws outdoors
When a joint starts to keep coming loose, the following guide, which explains the typical reasons why bolts loosen even when the correct torque is applied, will be helpful. In the case of situations involving constant movement, refer to the fasteners designed for high-vibration environments.
Why do self-tapping and self-drilling screws fail?
Failures tend to follow certain patterns, and by knowing these patterns you can draw up a better spec.
The majority of these cases can be traced to a specification that had a field left unspecified. The three fields most frequently omitted are the point number, the size of the pilot hole, and the coating.
Where are self-tapping and self-drilling screws used?
Order self-tapping and self-drilling screws to your specification
The majority of screw problems occur on site, at a distance from the drawing that caused them; an incorrect point number or the omission of a coating specification is passed on with every order until somebody climbs up the roof and discovers it.
Wootz.work operates at an upstream level in this area; it acts as a single accountable manufacturing partner to OEM buyers, brands and distributors, having one contract and one point of contact within a network of more than 400 qualified manufacturers in India and Southeast Asia. The company’s range of fasteners includes self-drilling and tech screws made from stainless steel, carbon steel, and alloy steel, and finished with zinc plating, hot-dip galvanizing, and Dacromet.
If you are asking for self-tapping, self-drilling screws, please include the material being used, the total thickness, the environment, and the type of driver together with your drawing. A design for manufacturability (DFM) review is carried out on the joint before a quote is given, so that the style and point are confirmed at an early stage. The page on design capabilities gives more information about this review, and quotes usually come within 24 to 48 hours.
There is one limitation. For a small quantity of ordinary catalog screws, a local distributor is generally the faster option. The partner network proves its value when it comes to repeated programs, special finishes, and custom specifications.
Conclusion: choose the screw by the joint, not the name
Self-tapping vs. self-drilling screws comes down to three checks: is there a hole, how thick is the steel, and where will the joint live. Match the screw to the joint, and the choice gets easier every time. Holes and thin material point to self-tapping. No holes and thicker steel point to self-drilling. Match the drill point to the total stack, pick the coating for the environment, and write all of it on the drawing.
Get self-tapping, self-drilling screws made to your drawing
Send us your drawing. Your first quote comes with a free DFM review. Talk to our engineering team about your program, download our fasteners catalog, or order a free sample box to check our finish and tolerances first.
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