Do self tapping screws need a pilot hole?

Yes, in metal. A self tapping screw cuts or forms its own threads but cannot drill through metal, so the hole must be pre-drilled slightly smaller than the screw. In very thin or soft material a sharp Type A point can pierce its own hole, but that is the exception. Self drilling screws are the ones that need no pilot hole.

Are Tek screws self tapping or self drilling?

Tek is a brand name for self drilling screws. They have a drill bit shaped point, bore their own hole, and then tap threads as the threads engage, so every self drilling screw is also self tapping, but a self tapping screw is never self drilling.

What do the point numbers on self drilling screws mean?

The number is the drill point length and capacity. A #2 point drills 0.036 to 0.210 inch of steel, #4 drills 0.125 to 0.250 inch, and a #5 point can drill and fasten up to 1/2 inch of steel. Bigger number, thicker material.

Self tapping vs self drilling screws

The two names get used interchangeably on job sites and even by some suppliers, which is exactly how the wrong box gets ordered ^[1] ^[2]. The difference is one sentence: a self tapping screw cuts its own threads in a hole you drilled; a self drilling screw drills the hole and then cuts the threads, in one pass ^[1] ^[3]. Everything else in this comparison, point numbers, thread types, and which one to buy for which material, falls out of that single distinction.

The difference in one look

	Self tapping	Self drilling (Tek)	Sources
Pilot hole	Required, pre-drilled slightly under screw diameter	None; the point is the drill	^{[1] [3] [4]}
Tip shape	Sharp point (Type A, AB) or blunt (Type B, F)	Twist drill point, numbered 1 to 5	^{[3] [4]}
What it does itself	Cuts or forms threads only	Drills the hole and taps threads	^{[1] [2]}
Material thickness	Thin sheet metal, plastics, wood	Light-to-medium gauge structural steel up to 1/2 in with a #5 point	^{[4] [5]}
Installation	Two steps: drill, then drive	One step: drive	^{[2] [5]}
Relationship	Self tapping, not self drilling	Self drilling, and therefore also self tapping	^{[3] [4]}

That last row is the logic knot worth untying: because a self drilling screw makes its own hole and then threads it, it is doing everything a self tapping screw does plus the drilling. Huyett and Birmingham Fastener both state the asymmetry plainly ^[3] ^[1]: all self drilling screws are self tapping; not all self tapping screws are self drilling. Tek is a brand name that has become shorthand for the self drilling type ^[2] ^[4].

Self tapping screws, in detail

The self tapping family splits by how the threads are made. Thread forming types push material aside: Type A with a sharp point and coarse threads, Type AB with a sharper point and finer threads, Type B with a blunt point, and High-Low designs with alternating thread crests for plastics. Thread cutting types actually remove material through flutes or cutting edges: Type BT and Type F for machine-screw threads, Type 23 and 25 with bigger cutting slots ^[3] ^[4]. The forming types are the common sheet-metal screws; the cutting types are what you reach for when the material cannot be displaced, such as brittle plastics or harder alloys.

The pilot hole rule is where self tapping screws succeed or fail. The hole must exist in metal and must be sized correctly: too small and the screw breaks or the material splits, too big and the threads strip and the joint is scrap ^[2] ^[3]. Governing standards exist, ANSI/ASME B18.6.4 for inch and B18.6.5 for metric, and they tabulate point types and pilot hole sizes by screw size ^[4]. For wood screws the same job is done by our pilot hole chart; for the metal side, the tap drill chart covers the machine-thread case where you cut threads with an actual tap.

Self drilling screws, in detail

The numbered point is the whole specification. The number communicates point length and therefore how thick a stack the screw can drill through, with larger numbers handling thicker material ^[3] ^[5]:

Drill point	Material thickness it drills	Sources
#1	0.018 to 0.095 in	^{[3] [5]}
#2 and #3	0.036 to 0.210 in	^{[3] [5]}
#4	0.125 to 0.250 in	^{[3] [5]}
#5	up to 1/2 in	^{[1] [3]}

One detail separates the crews who install wood-to-metal: wings. Some self drilling screws carry little tabs between the drill point and the threads that ream the wood oversize so the threads do not engage the wood and jack it off the steel before the head seats; the wings shear off when they hit the metal and the screw then tightens normally ^[3] ^[5]. Self drilling screws are still light-gauge fasteners at heart: metal roofing, steel framing, HVAC, cladding ^[2] ^[4]. Past half-inch steel the correct tool stops being a screw and becomes a pilot hole plus a structural bolt.

Which one to use

Thin sheet to thin sheet, lots of holes: self drilling, one-step installation saves the pilot pass ^[2] ^[5].
Metal framing and roofing: self drilling; this is the application the type was built for ^[2] ^[4].
Wood or plastic to metal: self drilling with wings, so the board clamps tight instead of threading up the shank ^[3] ^[5].
Very thin material: self tapping with a correct pilot hole; a drill point can over-enlarge a hole in ultra-thin stock and strip out ^[2] ^[5].
Existing holes, or plastics that need cut threads: self tapping, using the thread-cutting point types ^[3] ^[4].
Thicker structural steel: neither; drill and tap, or bolt. The #5 point ceiling is half an inch ^[1] ^[3].

Driving them without wrecking them

Both types live and die by RPM and clutch settings. A self drilling point has to reach cutting speed before the threads engage, or it burns; too fast and the point overheats and loses temper. The driver side of that balance, clutch numbers and when an impact driver is the wrong tool, is on our drill torque settings page, and the bit that actually transmits the torque is covered in screwdriver bit types. If the head needs to sit flush in wood, the recess geometry that makes that happen is on the countersink size chart page, which also carries the pilot-hole pairing for wood screws.

For pilot holes by wood screw gauge: pilot hole chart. For tapped threads in metal: tap drill chart. For flush heads in wood: countersink size chart. For the driver side: drill torque settings and screwdriver bit types.

Sources

Birmingham Fastener, Self-Drilling vs Self-Tapping: What's the Difference: pilot-hole requirement, point numbers 1 to 5, #5 point half-inch capacity, metal-building applications (bhamfast.com/blog/self-drilling-vs-self-tapping)
SendCutSend, Self-Drilling vs Self-Tapping Screws: What's the Best Fastening Solution: one-sentence distinction, pilot hole sizing consequences, Tek brand usage (sendcutsend.com/blog/self-drilling-vs-self-tapping-screws-whats-the-best-fastening-solution/)
Huyett, The Difference Between Self-Tapping and Self-Drilling Screws: point style taxonomy (Type A, AB, B, BT, F, 23, 25, High-Low), wing function, point number thickness tables (huyett.com/blog/difference-between-self-tapping-and-self-drilling-screws)
BDN Fasteners, Self-Tapping vs Self-Drilling Screws: What is the Real Difference: tip profiles, applications, thin-gauge guidance (bdnfasteners.com/what-the-difference-between-self-drilling-self-tapping-screws/)
Woodworking StackExchange, What is the difference between self-drilling and self-tapping screws: community technical corroboration of tip mechanics and pilot-hole behavior (woodworking.stackexchange.com/questions/14460)