SO / SOS / SOA Self-Clinching Through-Hole Standoffs
Through-hole self-clinching standoffs — SO (carbon steel), SOS (stainless steel) and SOA (aluminum) — fixed spacing with a fully through-threaded hole, metric M2 to M6, mounting holes Ø4.22–8.72 mm +0.03/0, minimum sheet 1.0–1.3 mm by size.
Last updated: 2026-11
Specifications
SO, SOS and SOA are through-hole self-clinching standoffs: the standoff presses into a thin sheet and holds a fixed spacing while offering a fully through-threaded hole, so a screw can pass through and engage beyond, or a mating part bolts down onto the standoff. The three codes share one geometry per thread size and differ in material: SO is carbon steel, SOS stainless steel, SOA aluminum. A typical designation reads SO-M3-8: an M3 x 0.5 through-hole standoff with an 8 mm nominal length. The collected installation table runs metric M2 x 0.4 through M6 x 1.0, including the supplier-specific "3.5M3" and "3.5M4" heavy-wall codes (supplier structure codes, not standard M3.5/M4 threads — keep the complete code on drawings and purchase orders). The collected guide notes that specifications may vary between domestic suppliers and that final production dimensions should follow the approved supplier drawing.
| Series | SO (carbon steel), SOS (stainless steel), SOA (aluminum) — through-hole standoffs with a fully through-threaded hole |
|---|---|
| Thread range | M2 x 0.4, M2.5 x 0.45, M3 x 0.5, 3.5M3 x 0.5, M4 x 0.7, 3.5M4 x 0.7, M5 x 0.8, M6 x 1.0 |
| Supplier-code note | "3.5M3" and "3.5M4" are supplier-specific heavy-wall structure codes, not standard M3.5/M4 threads — the complete code must be retained on engineering drawings and purchase orders |
| Minimum sheet thickness (by size) | 1.0 mm (M2–3.5M3); 1.3 mm (3.5M4–M6) |
| Mounting hole (by size) | Ø4.22 mm (M2–M3), Ø5.41 mm (3.5M3), Ø6.00 mm (M4), Ø7.14 mm (3.5M4 & M5), Ø8.72 mm (M6) — each +0.03/0 (controlled clinching hole) |
| Clinch-section diameter C (by size) | 4.20, 4.20, 4.20, 5.39, 5.98, 7.12, 7.12, 8.70 mm in the same thread order |
| External body dimension H (by size) | 4.8, 4.8, 4.8, 6.4, 7.0, 7.9, 7.9, 10.0 mm in the same thread order |
| Minimum edge distance (by size) | 6.0, 6.0, 6.0, 6.8, 7.5, 8.0, 8.0, 10.0 mm in the same thread order |
| Designation | SO-M3-8 = SO through-hole standoff, M3 x 0.5, 8 mm nominal length |
| Drawing caveat | Collected source notes specifications may vary between domestic suppliers — final production dimensions per the approved supplier drawing |
| MOQ / lead time | Not owner-confirmed for this family — confirmed at quotation |
Materials
- Carbon steel (SO series)
- Stainless steel (SOS series)
- Aluminum (SOA series)
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 (SO / SOS / SOA Self-Clinching Through-Hole Standoffs) 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 quantities and lead times for this family are confirmed at quotation — send your sizes, grades and quantities on the RFQ and the quote will carry a firm schedule. Sample availability is confirmed with the 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
Through-hole (SO) or blind (BSO) standoff — which do I need?
Both fix the same spacing and clinch into the same mounting hole per size. SO/SOS/SOA are through-threaded, so the mounting screw passes through and engages beyond the standoff — or a mating part bolts onto the standoff face. BSO/BSOS/BSOA are blind: the far end is closed, which controls how far the screw can penetrate. If the screw must not protrude or bottom into something behind the sheet, quote the blind series.
What do the C and H dimensions on a standoff drawing mean?
C is the clinching-section diameter that presses into the mounting hole (for example C 4.20 mm at M2–M3, 8.70 mm at M6); H is the external body dimension across the standoff (4.8 mm at M2–M3, 10.0 mm at M6). Both come straight from the installation table per thread size, along with the +0.03/0 mounting-hole tolerance. Keep the supplier's drawing as the final authority — the collected source itself flags that dimensions vary between suppliers.
What should an RFQ for these self-clinching standoffs or studs state?
State the series (FH/FHS stud, SO/SOS/SOA through-hole standoff, or BSO/BSOS/BSOA blind standoff), thread size and pitch (for example M4 x 0.7), nominal length L, sheet material and thickness, and — for blind standoffs — the required effective thread depth and the maximum permitted screw penetration. Quantity per size and destination country complete the RFQ. Commercial terms are confirmed at quotation.
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