Low Head Socket Cap Screw Dimensions — ASME B18.3 Inch Ladder (#8 to 1/2, Alloy)
Dimensions and mechanical properties for ASME B18.3 low head socket cap screws in the six sizes #8 through 1/2 — the reduced-head variant for clearance-limited assemblies — transcribed row-for-row from the collected chart.
Last updated: 2026-11
Specifications
Low head socket cap screws cut the head height to roughly two-thirds of the standard B18.3 head so the screw fits where a full-height cap screw would foul: shallow pockets, sliding covers, tooling plates stacked close together. The collected chart tabulates the ladder where the variant actually exists — six sizes, #8 through 1/2 — each with body and head diameter max/min pairs, head height, hex socket and key engagement, plus the two figures that separate this variant from the standard head: minimum tensile and the tightening torque. At 1/4 the low head runs 0.375 in head diameter (same as standard) on a 0.127 in height against the standard 0.250 — and its 5,250 lb minimum tensile and 77.9 in-lb torque sit below the standard head's 5,725 lb / 200 in-lb, the mechanical consequence of the thinner wall between socket and head. That trade is the whole selection argument: buy clearance with preload. The source states the same boundary the standard does — low heads cannot carry the same preload as standard heads of the same size — so joints designed around standard cap-screw torque tables do not transfer to this variant without re-checking. The ladder stops at #8 and 1/2 because that is where the variant's product line runs; below #8 or above 1/2, the standard head is the offering, per RFQ for anything unusual.
| Standard | ASME B18.3 — low head socket cap screws, inch series; 6-size ladder #8 through 1/2, alloy steel |
|---|---|
| Per-row data (in) | Body diameter max/min, head diameter max/min, head height, hex socket, key engagement — 1/4: body 0.2500/0.2435, head 0.375/0.369, height 0.127/0.121, socket 0.125 |
| Mechanical (alloy) | Tensile lbs min and tightening torque per size — 1/4: 5,250 lb UNRC / 6,000 lb UNRF, 77.9 in-lb; 1/2: 23,400 / 26,350 lb, 615.0 in-lb |
| Preload boundary | Reduced head height ⇒ lower allowable preload than the standard head of the same size — do not reuse standard-head torque tables (flagged on the page) |
| Size coverage | #8 to 1/2 only in the collected chart; other sizes per RFQ |
| Size | Basic Screw Dia. (D) Max | Body Dia. (F) Max | Body Dia. (F) Min | Head Dia. (A) Max | Head Dia. (A) Min | Head Height (H) Max | Head Height (H) Min | Hex Socket (J) Max | Key Engagement (T) Min | Tensile UNRC (lbs min) | Tensile UNRF (lbs min) | Tightening Torque (in.-lbs) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 8 | 0.1640 | 0.1640 | 0.1585 | 0.270 | 0.265 | 0.085 | 0.079 | 0.078 | 0.060 | 2,310 | 2,440 | 19.4 |
| 10 | 0.1900 | 0.1900 | 0.1840 | 0.312 | 0.307 | 0.098 | 0.092 | 0.094 | 0.072 | 2,890 | 3,300 | 33.5 |
| 1/4 | 0.2500 | 0.2500 | 0.2435 | 0.375 | 0.369 | 0.127 | 0.121 | 0.125 | 0.094 | 5,250 | 6,000 | 77.9 |
| 5/16 | 0.3125 | 0.3125 | 0.3053 | 0.437 | 0.431 | 0.158 | 0.152 | 0.156 | 0.110 | 8,650 | 9,550 | 156.0 |
| 3/8 | 0.3750 | 0.3750 | 0.3678 | 0.562 | 0.556 | 0.192 | 0.182 | 0.188 | 0.115 | 12,800 | 14,450 | 273.0 |
| 1/2 | 0.5000 | 0.5000 | 0.4919 | 0.750 | 0.743 | 0.254 | 0.244 | 0.250 | 0.151 | 23,400 | 26,350 | 615.0 |
- Row 1 (8): Ladder covers #8 through 1/2 only — the source chart does not extend the low-head ladder below #8 or above 1/2 in; larger sizes are per RFQ, not extrapolated.
| Thread Length Group | Up to 1 in. | Over 1 in. to 2-1/2 in. |
|---|---|---|
| Up to 1" (Inclusive) | Over 1" - 2-1/2" (Inclusive) | |
| 0 thru 3/8 | -.03 | -.04 |
| 1/2 | -.03 | -.06 |
| Nom. size | UNRC tensile (lbs. min.) | UNRF tensile (lbs. min.) | UNRC shear to 1" (lbs.) | UNRF shear to 1" (lbs.) | Recommended seating torque (inch-lbs.) |
|---|---|---|---|---|---|
| #8 | 2,380 | 2,500 | 1,450 | 1,570 | 25 |
| #10 | 2,980 | 3,400 | 1,700 | 2,140 | 35 |
| 1/4" | 5,410 | 6,180 | 3,090 | 3,900 | 80 |
| 5/16" | 8,910 | 9,870 | 4,930 | 6,210 | 157 |
| 3/8" | 13,200 | 14,900 | 7,450 | 9,400 | 278 |
| 1/2" | 24,100 | 27,200 | 13,600 | 17,100 | 667 |
Materials
- Alloy steel, quenched and tempered (~170,000 psi tensile class per the source); the chart is geometry data — state finish and environment 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 (Low Head Socket Cap Screw Dimensions — ASME B18.3 Inch Ladder (#8 to 1/2, Alloy)) 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
How much strength does the low head actually give up, and how do I spec it without under-torquing the joint?
Compare the two ladders at the same size and the cost of the clearance is visible: at 1/4 the low head carries 5,250 lb minimum tensile and 77.9 in-lb of tightening torque against the standard head's 5,725 lb and 200 in-lb — roughly 8% of strength but under half the allowable torque, because torque limits head failure (socket wall strip-out), not thread strength. That is the practical rule: the thread is nearly as strong as a standard screw, but the head is not, so the preload you can develop drops accordingly. Spec it by stating the size and letting the low-head torque column govern the assembly instruction — do not port the standard-head torque value, which will overload the reduced head. Choose this variant when the head height envelope genuinely binds (stacked plates, sliding hardware, shallow counterbores); when height is free, the standard head buys more preload for the same thread. The collected chart covers #8–1/2 in alloy only — stainless low heads, fine-thread torque figures and larger sizes are not tabulated, so they come back as RFQ answers rather than chart lookups.
What is the MOQ and lead time for socket screws referenced by these charts?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Confirm the exact schedule against quantity, size mix and finish 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