You can find many types of screws for different tasks. While many such as wood screws require pilot holes in thicker materials, others for sheet or thinner materials differ considerably. Self-tapping screws are a fantastic addition, as they are not as reliant on such an extent of a pilot hole.
Some self-tapping screws are also self-drilling, combining drilling-like action and fastener installation in one action. While you use the same principles as with other screws, they create their own holes with coarse threads.
Using soft materials, they can even pierce these with their sharp point to avoid drilling altogether. However, when used on roofing or sheet metal, the addition of a small hole size makes it far easier to install. (Read Tek Screw Sizes Chart)
Finding the right ones can be tricky so you can use our self-tapping screw size chart in our guide. By the end, you’ll know enough to quickly find the right screw size for all your fastening applications.
What Size Is A #10 Self-Tapping Screw?
A pilot hole must be bored before you can use most screws.
While self-drilling screws can drill their own hole, other types of tapping, thread cutting, thread shaping, and thread rolling screws require help to get started.
To enable insertion into the material, blunt-headed screws such as Type B Tapping, Type F Thread Cutting, and Thread Forming Screws for Plastics and Metals require the correct sizing.
If a pilot hole diameter isn’t appropriately sized, even sharp-pointed screws like Type A or Type AB Self-Tapping Screws might shred wood or bend metal as they’re pushed.
Type AB Self-Tapping Screws
| Screw Size | Screw Threads per Inch | Recommended Hole Diameter | Drill Bit Size |
|---|---|---|---|
| #2 | 32 | 0.0760" | #48 |
| #3 | 28 | 0.0810" | #46 |
| #4 | 24 | 0.0860" | #44 |
| #5 | 20 | 0.1065" | #36 |
| #6 | 20 | 0.1160" | #32 |
| #7 | 19 | 0.1285" | #30 |
| #8 | 18 | 0.1360" | #29 |
| #10 | 16 | 0.1590" | #21 |
| #12 | 24 | 0.1875" | 3/16" |
| 1/4" | 14 | 0.2188" | 7/32" |
| 5/16" | 12 | 0.2720" | I |
| 3/8" | 12 | 0.3281" | 21/64" |
Here are a few other things to consider when searching for the right self-drilling fasteners.
Drill Flute
The drill flute length controls the maximum metal thickness that you can drill. The drilled material can exit the hole thanks to drill flutes.
The drill chips will clog the flute and stop the cutting motion if the drill flute becomes immersed in the material. In addition, the heat from the drill chips could cause the drill point to overheat and fail if this happens. (Read Metric Allen Wrench Sizes)
Point Length
The unthreaded region between the drill point and the first thread is known as the drill point.
Before the threads engage, this length must be long enough to drill entirely through the material. This is because the threads can bind and shatter the fastener if they engage too early.
Screw Wings
When connecting wood to metal above 1/2″ thick, fasteners with wings are required. The wings will ream a clearance hole, preventing the threads from engaging too soon.
If the threads engage too early, the secured material may be separated from the base material.
The wings will break off as they strike the metal material, allowing the threads to engage. (Learn How To Unscrew a Rusted Screw)
Self-tapping screws and thread-forming screws
When self-tapping screws are screwed into plastic, wood, or metal, they tap their own threads, unlike ordinary screws. Thread forming and thread tapping are the two most common self-tapping screws.
Self-tapping screws are typically used to join two pieces of material where you may access only one side of the material. However, you can use a screw or a bolt where both sides are accessible.
Self-tapping screws help disassemble and reassemble objects as they are easily removed, and the fastener can be reinserted.
Self-tapping screws vs. self-drilling screws
It’s easy to mix up self-tapping with self-drilling screws. This is because self-tapping screws do not have an inbuilt drill bit, and certain varieties of self-tapping screws need drilling a pilot hole before being pushed into material.
The nose is blunt, and the end is flat.
Before self-tapping screws can be driven into the material with a screwdriver, a pilot hole diameter somewhat smaller than the screw must be made.
Self-tapping screws with a pointed nose do not require a pilot hole. Instead, the self-tapping screw will cut a thread into the material as it is driven in, holding it together.
Self-tapping screws are commonly used to join materials such as fastening wood, plastic, metal, and masonry.
Thread-forming and thread-cutting are the two types of self-tapping screws.
Thread-forming: Because these screws do not have a pointed tip, you will need to drill a pilot hole before using them. Plastic materials are held together with thread-forming screws.
They often hold material more tightly because of their design. However, care should be given because over-tightening the larger screw can cause the linked materials to crack because of the pressure.
Thread-Tapping: Although a pilot hole is not required for these screws, one can be bored to make fastening easier. Ensure the pilot hole is less than the thread tapping screw’s diameter.
Thread-tapping screws remove material while also creating a passage for the screw to travel through. The disadvantage of utilizing this type of screw is that it can cause stripped threads when removed. If you have stripped threads, reattachment should be done using a larger thread-tapping screw.
What Size Is a No 6 Self-tapping Screw?
Here you can find some popular types of self-tapping screws.
Countersunk or Flat Head
As the head of the screw sits below the surface of the surrounding material, it allows for a flush finish. This allows a flat surface and a smooth product.
Allen or Socket Head
Based on the shape of the driver used, the head of the screw is less likely to be compromised and distorted when driving into the material.
Bugle Head
The bugle head screw has a concave bearing face and a countersunk head with a flat top. The bugle head’s shape allows stress to be distributed across a considerably larger area than a flat head screw would.
Plasterboard is attached to wood and metal studs using bugle-headed screws.
Button Head
Typically found in carpentry. Due to the dome shape, the screw head is less likely to countersink into the material.
Flange Head
Metal to metal and plastic to plastic are the most common applications. When compared to other head types, the flanged head allows for higher clamping torque to be applied.
Hex Head
Contractors typically use these screws with a hexagonal head in heavy-duty situations where a countersunk head isn’t required.
Wafer Head
Wafer head screws have a countersunk head and a flat top surface. The conical under-head of the screw does not extend to the screw head’s outer edge, allowing for a flush fit on wood and other softer materials.
Pan Head
The top of this screw’s head is rounded, but the sides are vertical. They look like oval or circular screws. They’re typically employed in metal or wood applications that require a lot of torque.
Pancake Head
When a broad clamping area and an unobstructed head are required, this screw head is employed. Due to the bigger clamping area, the force is dispersed across a broader area.
Square Head
When driving a screw into the material, the bit is less likely to slip (cam-out) than a typical Phillips screw.
To avoid overtightening the screw, take care not to overtighten it.
Truss Head
This self-tapping screw head is extensive and has a slightly rounded top and a larger surface area beneath the screw head. (Learn How To Magnetize A Screwdriver)
Sheet metal and other materials with big diameter holes are suited for truss head screws. However, tampering with or removing the head is difficult due to its low-dome head.
Type A Self-Tapping Screws
| Screw Size | Screw Threads per Inch | Recommended Hole Diameter | Drill Bit Size |
|---|---|---|---|
| #2 | 32 | 0.0760" | #48 |
| #3 | 28 | 0.0810" | #46 |
| #4 | 24 | 0.0860" | #44 |
| #5 | 20 | 0.1065" | #36 |
| #6 | 18 | 0.1160" | #32 |
| #7 | 16 | 0.1285" | #30 |
| #8 | 15 | 0.1360" | #29 |
| #10 | 12 | 0.1590" | #21 |
| #12 | 11 | 0.1875" | 3/16" |
| #14 / 1/4" | 10 | 0.2188" | 7/32" |
| 5/16" | 9 | 0.2900" | L |
| 3/8" | 9 | 0.3438" | 11/32" |
What Do The Numbers On Self-tapping Screws Mean?
Type F Thread Cutting Screws – Type 1 Thread Cutting Screws – Type 23 Thread Cutting Screws
| Screw Size-TPI | Recommended Hole Diameter | Drill Bit Size |
|---|---|---|
| 2-56 | 0.0730" | #49 |
| 3-48 | 0.0810 | #46 |
| 4-40 | 0.0960" | #41 |
| 5-40 | 0.1010" | #37 |
| 6-32 | 0.1200" | #31 |
| 8-32 | 0.1470" | #26 |
| 10-24 | 0.1730" | #17 |
| 10-32 | 0.1770" | #16 |
| 12-24 | 0.1990" | #8 |
| 1/4-20 | 0.2280" | #1 |
| 5/16-18 | 0.2900" | L |
| 3/8-16 | 0.3580" | T |
| 1/2-13 | 0.4531" | 29/64" |
When using any of these, you need to be sure you have the suitable types of screwdriver, which is dictated by the drive tip for a specific head type on your chosen screw.
However, you can find some types of screwdrivers which are application-specific.
If you need Tek screws for wood, use roofing Tek screws. The flute on these screws is tiny, and the hole it drills is smaller than the external screw thread. This shape allows the screw to bite into the material securely.
Self-drilling screws have the same head and drive as self-tapping screws. Choose your screw type based on the material and finish.
The flute length defines the metal thickness that the self-drilling screw can use. The flute removes the drilled material. Cutting stops if the flute gets clogged. So, to require thick pieces of material, you will need a self-drilling screw with a flute. The drill point will likely overheat and fail if you ignore a clogged flute.
The drill point is the unthreaded section of the screw. When choosing the screw length, consider the material being drilled through. The screw breaks if the threads engage before the drill point length goes completely through the material.
When connecting wood over 0.5 inches thick to metal, use self-drilling screws with wings. The wings ream a clearing hole to stop threads engaging too early. When the wings touch the metal, they break off, allowing the threads to grip. If threads engage too early, the materials will separate. (Read Phillips Head Screwdriver Sizes Guide)
Self-drilling screws are as vulnerable as drill bits. The speed and depth of the cut affect cutting performance. Select the suitable screw size for your application to avoid the drill bit melting or less chance of snapping because of excessive RPM or pressure.
Smaller diameter screws can withstand greater RPMs but require less effort. The wider the screw diameter, the lower the RPM, but, the higher the force, which is better for high torque applications.
With over 20 years of hands-on gardening and landscape design experience, Tim Graham, the founder of YardandGardenGuru.com, is dedicated to sharing expert advice and fostering a vibrant community for garden enthusiasts. His award-winning designs and sustainable practices reflect a deep-rooted passion and expertise in horticulture. Connect and cultivate your green thumb with Tim!