Self-Tapping Screws: GB 845, DIN 7981 and DIN 7982
What makes a screw self-tapping
A self-tapping screw cuts or forms its own thread in the material it enters. There is no nut, no pre-tapped hole and usually no machine screw partner at all: the fastener is the thread. That single property splits into two behaviours worth knowing before you order:
- Thread-forming screws displace material — the norm in plastics and thin sheet, where the screw squeezes into a pilot hole and the elastic recovery of the plastic locks it. Most of the screws on this page are thread-forming.
- Thread-cutting screws have a cutting slot or flute and remove material instead — used where the boss would crack or where the joint must be reopened many times.
The practical consequence: the pilot hole, not the screw, decides whether the joint works. Too small and the boss splits; too large and the screw strips on the first tightening. That is the opposite of a machine screw, where the tapped hole is cut to the thread’s own dimensions.
GB 845, DIN 7981 and ISO 7049: the same pan head screw
The three designations buyers search for most often are one product. GB/T 845 is the Chinese national standard for a cross recessed pan head tapping screw — the GB 845 page lists the stocked matrix; ISO 7049 is its international equivalent; DIN 7981 is the German number for the same head form, now generally cross-referenced to the ISO standard. The countersunk versions follow the same pattern:
| Head form | Chinese | ISO | DIN |
|---|---|---|---|
| Cross recessed pan head | GB/T 845 | ISO 7049 | DIN 7981 |
| Cross recessed countersunk | GB/T 846 | ISO 7050 | DIN 7982 |
| Cross recessed oval head | GB/T 847 | ISO 7051 | DIN 7983 |
| Hex head wood screw | GB 102 | — | DIN 571 |
| Self-drilling (drill point) | GB 15856.1–4 | — | DIN 7504 |
If your drawing says DIN 7981 and your supplier quotes GB 845, the parts interchange within the tolerances of the standard. If it says DIN 7982 and you get GB 845, you have a head that will not sit flush. The wider Chinese-ISO-DIN mapping is in the standards comparison chart.
ISO 7049 dimensions, ST2.2 to ST9.5
Tapping screws are designated ST rather than M, and the ISO series runs from ST2.2 to ST9.5. Nominal values below; dk is head diameter, k is head height, and the recess number is the Phillips bit size.
| Size | Pitch (mm) | Head dia. dk max (mm) | Head height k max (mm) | Recess No. |
|---|---|---|---|---|
| ST2.2 | 0.8 | 4.0 | 1.6 | 0 |
| ST2.9 | 1.1 | 5.6 | 2.4 | 1 |
| ST3.5 | 1.3 | 7.0 | 2.6 | 2 |
| ST4.2 | 1.4 | 8.0 | 3.1 | 2 |
| ST4.8 | 1.6 | 9.5 | 3.7 | 2 |
| ST5.5 | 1.8 | 11.0 | 4.0 | 3 |
| ST6.3 | 1.8 | 12.0 | 4.6 | 3 |
| ST8 | 2.1 | 16.0 | 6.0 | 4 |
| ST9.5 | 2.1 | 20.0 | 7.5 | 4 |
The ISO series has no ST1.7, ST2.6 or ST2.3 — and those are exactly the sizes the electronics trade buys most. In southern China they come from the regional Yuebiao standards for tapping screws (our own sub-categories carry the names YB845 and YB846), which extend the ladder below ST2.2: 1.2, 1.4, 1.7, 2.2, 2.6, 3.5, 4.2, 5.5 mm nominal. Our catalogue labels those diameters with an M prefix (M1.7, M2.3, M2.6, M4.2, M5.5) because that is what a Chinese BOM and a Chinese factory both use, while some items carry the ST prefix (ST3 appears on 18 part numbers). They are all tapping screws; the prefix is a labelling habit, not a different thread.
Why our sizes read “M2.6” and “ST3”
So the letter in front of the number tells you which labelling tradition the supplier works in, not what the thread is. That matters when two quotes for “M2.6 tapping screws” come back with different head diameters — one may be quoting a regional-standard part and the other an ST2.6 that does not exist in ISO 7049 at all.
What matters is that you match on the number, not the letter. Below M3 the spread is the widest of any category we hold:
| Size | Part numbers | Size | Part numbers |
|---|---|---|---|
| M4 | 500 | M2.3 | 178 |
| M3 | 450 | M1.7 | 147 |
| M5 | 389 | M8 | 134 |
| M6 | 346 | M1.4 | 96 |
| M3.5 | 326 | M10 | 77 |
| M2 | 256 | M1.2 | 69 |
| M2.6 | 225 | M2.2 / M5.5 | 50 / 49 |
If you need tapping screws below M1.7, the sizes exist here but are thin — 45 part numbers at M1.0, 69 at M1.2. The micro screws guide explains the machine-screw equivalent of that size range, and the difference in thread form matters: a machine screw will not hold in a plastic boss the way a tapping screw does.
Which head styles we actually stock
Head form, not standard number, is what most buyers are really choosing. Counted across the 3,677 lines in the self-tapping screws category:
| Head / type | Part numbers | Where it is used |
|---|---|---|
| Cross recess pan head | 1,441 | The default; largest bearing face, sits on the surface |
| Cross recess countersunk | 856 | Flush finish, thin panels |
| JIS B 1122T truss head (TA) | 309 | Wide low head, Japanese-designed appliances and electronics |
| Hex head wood screw (DIN 571) | 172 | Timber, coach-screw style, driven with a socket or spanner |
| Slotted / flat head patterns | 174 | Legacy and decorative work |
| Washer head (PWA / PWB) | — | Built-in washer spreads load on soft sheet |
| Socket head (KCA / PCA) | — | Hex key drive, higher torque, tamper resistance |
| Eye, double-ended, Hi-Lo, quick-thread | — | Specialty: hanging, spacers, plastics, fast assembly |
Two of those deserve a sentence. The truss head has the widest diameter-to-height ratio of any common head, which is why Japanese appliance designs use it over plastic: same clamp load, less point pressure. And Hi-Lo thread — alternating high and low threads — is the standard answer for brittle plastics, because the low thread reduces hoop stress while the high thread still holds.
DIN 571 is a wood screw, not a sheet-metal screw
It sits in this category on our site because buyers search “tapping screw” for it, but DIN 571 is a hex head wood screw: coarse thread, tapered point, hex drive, meant for timber and heavy carpentry. The thread pitch is far coarser than any ST size, so it pulls into softwood without a pilot hole and resists pull-out under load. Do not substitute it for a pan head tapping screw in sheet metal — the coarse thread will not form a reliable thread in 1 mm steel. All 172 of our DIN 571 lines are listed together on the DIN 571 page.
Materials and finishes
Stainless dominates: 1,531 part numbers in 304, 320 in 316, against 1,713 in carbon steel (1010, 1022, 1022A and Q195 grades), plus 85 in brass. The finish split matters more than the steel for outdoor work — 1,807 lines are plain (uncoated), 684 nickel plated, 376 black zinc, 275 black oxide, 211 blue-white zinc. For exterior or washdown use, 316 with no coating beats 304 with a coating every time; the reasoning is in A2-70 vs grade 8.8, and the seizing risk in stainless-to-stainless joints is covered in the galling guide.
Ordering self-tapping screws
Everything here is priced per piece in USD with no minimum order, packed from our own warehouse within 24–48 hours. Three things to put on the enquiry if you want a first-time-right quote: the material to be tapped (plastic grade or steel thickness), the head form, and whether the point is a sharp C-type or a blunt F-type — the point type decides whether the screw can start without a pilot. If the item is a machine screw you actually need, start from the GB 818 guide instead; and if the thread data is what you are checking, the metric thread pitch chart covers every coarse and fine series.
FAQ
Is GB 845 the same as DIN 7981?
Yes in form: GB/T 845, ISO 7049 and DIN 7981 all describe a cross recessed pan head tapping screw, and parts interchange within standard tolerances. The DIN number is now generally cross-referenced to ISO 7049.
What is the difference between DIN 7981 and DIN 7982?
The head. DIN 7981 is pan head — it sits on top of the surface. DIN 7982 is countersunk (GB/T 846 / ISO 7050) — it sits flush, which requires a matching countersink in the panel.
Are ST and M sizes the same for tapping screws?
Not quite. ISO 7049 and JIS B 1122 both run the ST series from ST2.2 to ST9.5. The smaller diameters the electronics trade uses — 1.2, 1.4, 1.7, 2.2, 2.6 mm — come from the regional Yuebiao practice and appear in our catalogue with an M prefix. Match the number, and confirm head diameter before substituting.
What size pilot hole do I need?
For thread-forming screws the pilot must be smaller than the nominal diameter — roughly the minor diameter of the screw, adjusted for material. In plastics, start at about 0.8 × nominal diameter and test on a sample boss; in sheet metal, drill to the screw’s minor diameter. Always test the first joint rather than trusting a table.
Do you stock self-drilling screws?
Only a small drywall range: 16 lines under GB 14210 (drywall screws). For drill-point screws to DIN 7504 / GB 15856, ask for a quote — they are produced to order rather than held on the shelf.
What is a truss head TA screw?
A cross recessed truss head tapping screw to JIS B 1122 — a very wide, low head that spreads clamp load over a large area. We stock 309 part numbers, mostly 304 stainless, in the sizes used by Japanese appliance and electronics designs.
Can self-tapping screws be reused?
In metal, once or twice at most — each reinsertion cuts a slightly larger thread and the grip falls away. In plastic, a thread-forming screw loses hold after two or three cycles because the formed thread deforms permanently; for serviceable joints use a thread-cutting screw or a metal insert.