ISO 1478 Self-Tapping Screw Threads (ST) — Thread and Point Dimensions, ST 1.5 – ST 9.5 (mm)
ISO 1478 self-tapping screw thread (ST) dimensions — pitch, major/pitch/minor diameter max/min, crest rounding, point radius and incomplete-thread lengths for tapping types C, F and R per size from ST 1.5 to ST 9.5, transcribed row-for-row from the collected chart.
Last updated: 2026-11
Specifications
Self-tapping screws cut or form their own mating thread, and ISO 1478 defines the thread they carry: the ST series, sized ST 1.5 through ST 9.5. The collected chart's columns describe a thread optimized to cut rather than to run against a nut: d1 major max/min (ST 4.2: 4.22/4.04 mm), d2 pitch, d3 minor, and c crest rounding — a hardened thread whose sharp flanks and lobed cross-section do the tapping. The point columns are the practical heart of the chart: r the point radius (reference — the source notes the end may not be perfectly spherical but shall not be sharp), and y the length of incomplete thread at the point for the three tapping styles — type C (the cutting chip-clearence point), F (cutting with a machine-screw point) and R (forming/rolling, which displaces rather than removes material) — reading ST 4.2: y runs 3.7 mm (C), 2.8 (F), 3.2 (R). That length is engagement-critical: the incomplete thread is what does the tapping, so the screw must pass fully through the material being tapped before complete thread engages the host — hole depth and screw length are chosen around y. The former No. column (source Note 3) bridges old drawings ("No. 8 self-tapper" = ST 4.8). Host material, hole preparation and drive style are not tabulated — per RFQ; the source chart is presented transposed here, one row per size, with its "-" cells flagged on the table.
| Standard | ISO 1478 — self-tapping screw threads (ST series), thread and point dimensions; the ST thread is the common geometry across tapping types C (cutting), F (cutting, machine-screw point) and R (forming) |
|---|---|
| Size range | ST 1.5 – ST 9.5, 14 sizes; pitches 0.5 – 2.1 mm; dimensions in millimetres; former thread No. carried per size (information, source Note 3) |
| Tabulated thread (mm) | Per size: P ≈, d1 major max/min, d2 pitch max/min, d3 minor max/min, c crest rounding max; example ST 4.2: 1.4, 4.22/4.04, 3.10/2.95, 2.84/2.69, 0.1 |
| Point columns (mm, ref) | r point radius ≈ (may not be perfectly spherical but shall not be sharp — source Note 1); y incomplete-thread length per tapping type: C 3.7, F 2.8, R 3.2 at ST 4.2 (source Note 2) |
| Host material / holes | Substrate, drilled-hole or pilot sizing and drive style not tabulated by the collected chart — per RFQ |
| Thread Size | P ≈ | d1 — Major (max) | d1 (min) | d2 — Pitch (max) | d2 (min) | d3 — Minor (max) | d3 (min) | c (max) | r ≈ (ref) | y — Type C (ref) | y — Type F (ref) | y — Type R (ref) | Former No. (info) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ST 1.5 | 0.5 | 1.52 | 1.38 | 0.91 | 0.84 | 0.79 | 0.69 | 0.1 | - | 1.4 | 1.1 | - | 0 |
| ST 1.9 | 0.6 | 1.90 | 1.76 | 1.24 | 1.17 | 1.12 | 1.02 | 0.1 | - | 1.6 | 1.2 | - | 1 |
| ST 2.2 | 0.8 | 2.24 | 2.10 | 1.63 | 1.52 | 1.47 | 1.37 | 0.1 | - | 2 | 1.6 | - | 2 |
| ST 2.6 | 0.9 | 2.57 | 2.43 | 1.90 | 1.80 | 1.73 | 1.60 | 0.1 | - | 2.3 | 1.8 | - | 3 |
| ST 2.9 | 1.1 | 2.90 | 2.76 | 2.18 | 2.08 | 2.01 | 1.88 | 0.1 | - | 2.6 | 2.1 | - | 4 |
| ST 3.3 | 1.3 | 3.30 | 3.12 | 2.39 | 2.29 | 2.21 | 2.08 | 0.1 | - | 3 | 2.5 | - | 5 |
| ST 3.5 | 1.3 | 3.53 | 3.35 | 2.64 | 2.51 | 2.41 | 2.26 | 0.1 | 0.5 | 3.2 | 2.5 | 2.7 | 6 |
| ST 3.9 | 1.3 | 3.91 | 3.73 | 2.92 | 2.77 | 2.67 | 2.51 | 0.1 | 0.6 | 3.5 | 2.7 | 3 | 7 |
| ST 4.2 | 1.4 | 4.22 | 4.04 | 3.10 | 2.95 | 2.84 | 2.69 | 0.1 | 0.6 | 3.7 | 2.8 | 3.2 | 8 |
| ST 4.8 | 1.6 | 4.80 | 4.62 | 3.58 | 3.43 | 3.30 | 3.12 | 0.15 | 0.7 | 4.3 | 3.2 | 3.6 | 10 |
| ST 5.5 | 1.8 | 5.46 | 5.28 | 4.17 | 3.99 | 3.86 | 3.68 | 0.15 | 0.8 | 5 | 3.6 | 4.3 | 12 |
| ST 6.3 | 1.8 | 6.25 | 6.03 | 4.88 | 4.70 | 4.55 | 4.34 | 0.15 | 0.9 | 6 | 3.6 | 5 | 14 |
| ST 8 | 2.1 | 8.00 | 7.78 | 6.20 | 5.99 | 5.84 | 5.64 | 0.15 | 1.1 | 7.5 | 4.2 | 6.3 | 16 |
| ST 9.5 | 2.1 | 9.65 | 9.43 | 7.85 | 7.59 | 7.44 | 7.24 | 0.15 | 1.4 | 8 | 4.2 | - | 20 |
- Row 1 (ST 1.5): The source prints "-" for the r reference radius at ST 1.5 – ST 2.6 and for Type R incomplete-thread length below ST 3.5 and at ST 9.5 — those values are not offered by the collected chart, not zeros.
Materials
- Tapping type and host material go together — C/F cut (chips), R forms (no chips, needs ductility); specify host, type and finish together at RFQ
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ISO 1478 Self-Tapping Screw Threads (ST) — Thread and Point Dimensions, ST 1.5 – ST 9.5 (mm)) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
Type C, F or R self-tapper — what does the choice change, and why does the incomplete-thread length (y) drive hole design?
The tapping type decides how the joint is made and what the host must tolerate. Type C is the classic thread-cutting point: it cuts a chip-clearence thread as it enters, works across a broad range of metals and plastics, and leaves chips — fine in through-holes, a factor in blind holes where chips pack. Type F cuts with a machine-screw point: it suits thicker sections and rework (a stripped thread can often be re-entered with a larger F), with the same chip behavior. Type R thread-forms: it displaces the host material into a flowed thread, no chips, stronger in ductile hosts (the flowed thread work-hardens the host around the screw) — but it needs sufficient ductility, so brittle materials and some cast alloys are C/F territory. The chart's y column is why hole design follows the screw: the incomplete thread at the point (3.7 mm at ST 4.2 type C) is the working part that cuts or forms — the screw must traverse the full material thickness within y plus the thread pitch before its complete thread engages, so blind-hole depth, screw length and grip are calculated from y, not guessed. Practical specification: name host material, thickness and tapping type together — ST sizes are interchangeable across types only in thread geometry, not in what they do to the hole — and confirm hole preparation at RFQ; the chart's "-" cells (r below ST 2.6, y-R below ST 3.5) mean the source offers no reference value there, not that the dimension is zero.
What is the MOQ and lead time for threaded parts on this standard?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Common thread sizes on this standard are widely stocked; confirm the exact schedule against quantity and size mix at quotation.
Related knowledge
- Thread-Forming vs Thread-Cutting vs Thread-Rolling Self-Tapping Screws: What the Evidence Settles on Base Material
- Screw Family Selection by Base Material: Wood, Machine and Self-Tapping Threads, Engagement and Coating
- Hex Bolts vs Socket Head Cap Screws: What the Evidence Settles on Strength, Clearance and Cost
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support