A self-tapping screw makes its own thread, and the end of the screw decides how: a pointed type C end for thin sheet, a flat type F end for a pre-drilled hole, a cutting slot for thick or brittle material, a drill point for steel with no hole at all, and a tri-lobular form that rolls a thread into metal or plastic without cutting anything. The catalogue stocks all of them in the common sizes; the screw for an unusual material, a length between the steps, or a head sized for a slot is the one that gets made.
EKINSUN LTD is a custom parts manufacturer that turns tapping screws to drawing when the stock series stops: a length or head outside the range, a thread form for a plastic or an alloy the series was not designed for, a shoulder or a dog point, a material such as 316L, brass or PEEK. The size table below translates the ST sizes to the M sizes stock lists use; the end table matches the screw end to the material; the negative-space table marks the border between buying and making.
"Countersunk tapping screws for a 12 mm glass-filled nylon boss: every stock screw either cracks the boss or strips on the second assembly."
Glass-filled plastic is where standard tapping threads stop working and thread-forming screws for plastics begin.
| ST size (ISO 1478) | Sold as | Common heads in stock | Typical sheet |
|---|---|---|---|
| ST2.2 | M2 | pan PA, countersunk KA | 0.5–1 mm |
| ST2.9 | M3 | pan, countersunk, truss, pan washer | 0.7–1.5 mm |
| ST3.5 | M3.5 | pan, countersunk | 0.8–2 mm |
| ST3.9 / ST4.2 | M4 | pan, countersunk, truss, hex washer | 1–2.5 mm |
| ST4.8 | M5 | pan, countersunk, hex washer | 1.2–3 mm |
| ST5.5 | M5.5 | hex washer (self-drilling) | 1.5–4 mm |
| ST6.3 | M6 | pan, hex washer, hex | 2–5 mm |
| ST8 | M8 | hex | 3–6 mm |
Stock: pan PA M1–M8, countersunk KA M1–M8, truss TA M2–M6.3, large pan BA M2–M3, thin CA M2–M6, pan washer PWA M1.2–M5, hex washer M3–M6.3, socket-cap HA M1.7–M6, button PCA M2–M6, countersunk socket KCA M2–M6, Torx pan and countersunk M2–M6, in A2 and zinc steel; brass M2–M8. Sheet thicknesses are indicative for steel.
| End | Stock code | Standard | Material | Hole |
|---|---|---|---|---|
| Pointed (type C / AB thread) | A: PA, KA, TA, BA, CA | ISO 1478 type C; ISO 7049 / 7050 / 7051 | thin steel and aluminium sheet, soft plastics, wood | pilot hole or pierced; the point starts the thread |
| Flat end (type F / B thread) | B: PB, KB, TB, CB | ISO 1478 type F | thicker sheet, castings, plastics with a moulded hole | pre-drilled to the maker's table; no point to wander |
| Cutting end (BT / type 25) | T: PT, KT, TT, BT | maker series | thick, hard or brittle: die castings, hard plastics, phenolic | pre-drilled; the slot cuts chips and lowers driving torque |
| Drill point (self-drilling) | — | ISO 15480 (hex washer), 15481 (pan), 15482 (countersunk); DIN 7504 K / N / P | steel and aluminium sheet, purlins, roofing; 410 stainless or zinc steel | no hole; the drill point number sets the thickness it drills |
| Tri-lobular thread-forming | — | DIN 7500 (Taptite-type) | steel, aluminium, brass; rolls a metric thread a machine screw can follow | pilot near the pitch diameter; no chips |
| Thread-forming for thermoplastics (PT-type) | — | maker series | ABS, PC, PA, PBT, glass-filled grades | moulded boss hole; 30° flank and deep thread avoid boss stress |
| Chipboard and drywall | — | DIN 7997; DIN 18182 | wood, particleboard, plasterboard | no pilot in soft board |
| Hardened fibre and concrete nails | — | maker series | masonry, fibreboard | stock only |
A tapping screw with the wrong end is the commonest field failure in plastics: a pointed steel screw in a glass-filled boss cuts the boss instead of forming it. Send the plastic grade and the boss size before the screw size.
| What you need | In the catalogue? | What we make |
|---|---|---|
| Pan, countersunk or truss tapping screw ST2.2–ST6.3 in A2 or zinc steel, stock length | Yes | Buy it from stock. No one-off competes with a rolled tapping screw. |
| Self-drilling screw 3.5–6.3 mm in 410 stainless or zinc steel, with or without EPDM washer | Yes | Stocked; buy it. |
| Thread-forming DIN 7500 M3–M6 in pan, countersunk, hex flange, Torx | Yes | Stocked in zinc and nickel steel; buy it. |
| A tapping screw longer than the stock lengths, or with a plain shank section | No | Turned from bar with the tapping thread cut to the standard form, from 1 piece. |
| A head diameter or drive the series does not pair with that size | No | Head and recess machined on the turned screw. |
| A tapping screw in 316L, brass above M8, titanium or PEEK | No | Same thread form, your material; PEEK tapping screws for insulating assemblies. |
| A thread-forming screw for a glass-filled plastic in a size the PT series does not run | No | Turned with the 30° flank form to the boss. |
| A tapping screw in aluminium 6061 or 7075 | No | Not offered: an aluminium tapping thread strips in anything harder than soft plastic, and we say so; use a 7075 machine screw in an insert instead. |
| Material | Designation | Where it fits here |
|---|---|---|
| Stainless 304 | 1.4301 / A2 | stock tapping screws in every head; not self-drilling (too soft to drill) |
| Stainless 410, hardened | 1.4006 | stock self-drilling screws 3.5–6.3 mm |
| Stainless 316L | 1.4404 / A4 | turned to order for marine and chemical assemblies |
| Carbon steel, case-hardened | zinc, nickel, phosphate | stock tapping, self-drilling, chipboard and drywall screws |
| Brass | CW614N / CuZn37 | stock M2–M8 tapping screws; turned above |
| PEEK, nylon 66 | PEEK, PA66 | insulating tapping screws — see plastic fasteners |
| Aluminium 6061 | AlMg1SiCu | the sheet the screw goes into, not the screw |
| Aluminium 7075 | AlZn5.5MgCu | machine screws into inserts, not tapping screws |
AB (ISO 1478 type C) has a pointed end and a fine spaced thread for thin sheet; B (type F) has a flat end for pre-drilled holes in thicker material; BT (type 25) is a B thread with a cutting slot at the tip for thick, hard or brittle material. Stock lists mark them A, B and T after the head letter.
ST is the ISO 1478 tapping-screw thread designation and 4.2 is the nominal diameter in millimetres; stock lists usually print it as M4. ST2.9 is sold as M3, ST4.8 as M5, ST6.3 as M6.
Yes, but the end and thread form must suit the plastic: pointed screws work in soft ABS and PP, while glass-filled nylon, PBT and PC need thread-forming screws with a 30-degree flank (PT-type) so the boss is not cracked. For repeated assembly, a threaded insert is the durable answer.
Because the drill point has to be harder than the steel it drills, and 410 can be hardened while 304 cannot. 410 is less corrosion-resistant than 304, so stock self-drilling screws for outdoor use are often zinc-coated 410 or carbon steel with a zinc-flake finish.
EKINSUN LTD is a custom parts manufacturer that turns tapping, thread-forming and drill-point screws in 304, 316L and 410 stainless, steel, brass and PEEK, with the length, head, drive and thread form the assembly needs, from 1 piece, with a quote within 12 hours.
No list price; the drivers are material, the thread form, head and drive machining, and quantity. A batch of A2 tapping screws in an odd length is a short lathe job; a single PEEK thread-forming screw for a glass-filled boss is a small precision part and priced as one. The quote names the drivers.
Material and thickness of the part, hole type, screw end, head and drive, length, screw material, quantity. A photo of the boss or sheet with a rule works. From 1 piece, quote within 12 hours.
Tapping and thread-forming screws turned to end, head, drive, length and material — from 1 piece, quote in 12 hours.