BSO / BSOS / BSOA Self-Clinching Blind Standoffs
Blind self-clinching standoffs — BSO (carbon steel), BSOS (stainless steel) and BSOA (aluminum) — fixed spacing with a closed threaded end that controls screw penetration, metric M2 to M6, effective thread depth F ≥ 3.2 mm at L 6 up to F ≥ 9.5 mm at L 18–25 mm.
Last updated: 2026-11
Specifications
BSO, BSOS and BSOA are the blind counterparts of the through-hole SO series: the same clinching into a thin sheet and the same mounting dimensions per thread size, but the far end is closed, so the standoff holds a fixed spacing while the blind internal thread controls how far the mounting screw can penetrate — the screw must not bottom out before the joint is fully tightened. BSO is carbon steel, BSOS stainless steel, BSOA aluminum; a typical designation reads BSO-M3-8, the blind version of SO-M3-8. For the common metric BSO series the collected guide tabulates a minimum effective thread depth F by nominal length: L 6 mm → F ≥ 3.2 mm; L 8 or 10 mm → F ≥ 4.0 mm; L 12 mm → F ≥ 5.0 mm; L 14 or 16 mm → F ≥ 6.5 mm; L 18–25 mm → F ≥ 9.5 mm. The same guide's supplier caveat applies: specifications may vary between domestic suppliers, and final production dimensions follow the approved supplier drawing.
| Series | BSO (carbon steel), BSOS (stainless steel), BSOA (aluminum) — blind standoffs with a closed threaded end |
|---|---|
| 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 (same mounting table as the SO through-hole series) |
| Mounting data (per size) | Same as through-hole series: minimum sheet 1.0–1.3 mm; mounting hole Ø4.22–8.72 mm +0.03/0; clinch-section C 4.20–8.70 mm; body H 4.8–10.0 mm; edge distance 6.0–10.0 mm |
| Effective thread depth F (blind, by length L) | L 6 mm → F ≥ 3.2 mm; L 8 / 10 mm → F ≥ 4.0 mm; L 12 mm → F ≥ 5.0 mm; L 14 / 16 mm → F ≥ 6.5 mm; L 18 / 20 / 22 / 25 mm → F ≥ 9.5 mm |
| Blind-assembly rule | The drawing must specify effective thread depth and maximum permitted screw penetration; the screw must not bottom out before the joint is fully tightened |
| Designation | BSO-M3-8 = BSO blind standoff, M3 x 0.5, 8 mm nominal length |
| Sampled inch part (named part only) | Captive Fastener CFBSO6440-34 (blind standoff, #4-40 x 1.0625, heat-treated steel, zinc clear): sheet min 0.040 in.; hole 0.213 +0.003/−0.000 in.; L 1.062 +0.002/−0.005 in.; min thread depth T 0.375 in.; pushout 420 lbs / torque-out 35 in.-lbs / installation force 3300 lbs in 0.060 in. CRS (300 lbs / 25 in.-lbs / 1700 lbs in 0.060 in. 5052-H34 aluminum) |
| 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 (BSO series)
- Stainless steel (BSOS series)
- Aluminum (BSOA 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 (BSO / BSOS / BSOA Self-Clinching Blind 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
Why does the effective thread depth matter more on a blind standoff?
Because the far end is closed, the screw stops when it reaches the bottom of the blind hole — not when the joint is tight. The collected guide tabulates the minimum effective thread depth F by nominal length (L 6 mm → F ≥ 3.2 mm, L 12 mm → F ≥ 5.0 mm, L 18–25 mm → F ≥ 9.5 mm), and the assembly rule is explicit: the drawing must also state the maximum permitted screw penetration so the screw never bottoms out before the joint is fully tightened. If your screw engagement exceeds the table's F for the length you want, move up a length or confirm a custom on the RFQ.
What performance can I expect from an installed blind standoff?
The collected part-level datasheet for one named inch part (Captive Fastener CFBSO6440-34, #4-40 x 1.0625 blind standoff) tabulates, in 0.060 in. cold-rolled steel: 420 lbs pushout, 35 in.-lbs torque-out, 3300 lbs installation force, 380 lbs pull-through, with a maximum nut-tightening torque of 4.75 in.-lbs; the same part in 0.060 in. 5052-H34 aluminum shows 300 lbs / 25 in.-lbs / 1700 lbs / 310 lbs. These are that part's tested figures at that sheet thickness — not a series guarantee. Ask for the performance row of your exact series, thread and sheet at quotation.
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