ISO 7379 Socket Head Shoulder Screw A2 Stainless

FULLERKREG ISO 7379 A2 Stainless Steel Socket Head Shoulder Screws

FULLERKREG ISO 7379 A2 Stainless Steel Socket Head Shoulder Screws are precision corrosion-resistant fasteners with a unique three-part geometry: a cylindrical socket head, a precision-ground smooth shoulder (body), and a reduced-diameter threaded end. Manufactured from A2 (SUS304) austenitic stainless steel with a passivated natural finish, the shoulder is precision-ground to h6 tolerance, providing an accurate bearing surface for pivots, guides, linkages, and rolling element bearings. The combination of precision h6 shoulder geometry and A2 stainless steel corrosion resistance makes these screws the preferred choice for food processing, medical, outdoor, and corrosion-sensitive precision pivot applications.

Product Specifications

• Standard: ISO 7379
• Material: A2 Stainless Steel (SUS304 / 18-8)
• Strength Grade: A2-70
• Tensile Strength: Min. 700 MPa
• Proof Load Stress (Rp0.2): Min. 450 MPa
• Hardness: ≤95 HRB (max. 210 HV)
• Shoulder Diameter Tolerance: h6 (precision ground)
• Thread: Metric coarse, reduced diameter (smaller than shoulder)
• Thread Tolerance: 6g
• Drive Type: Hexagon socket (Allen key / hex key)
• Surface Treatment: Passivation — natural silver finish (pickling & passivation)
• Shoulder Sizes Available: φ5 – φ20 mm

Understanding Shoulder Screw Geometry

A shoulder screw has three distinct sections, each with a specific function:

Section	Description	Function
Head	Cylindrical socket head (knurled)	Drive and clamping — seats against mating surface
Shoulder (Body)	Precision-ground smooth cylinder, h6 tolerance	The functional element — pivot axis, guide pin, bearing race
Thread	Reduced diameter, shorter than shoulder	Fastening into tapped hole — pulls head down to clamp

Key principle: The thread diameter is always smaller than the shoulder diameter. The shoulder bears the load; the thread only provides clamping force. The component mounted on the shoulder (bearing, bushing, link) rotates or slides on the shoulder, not on the thread.

A2 Stainless vs Grade 12.9 Alloy Steel — Selection Guide

Property	A2 Stainless (This Page)	Grade 12.9 Alloy Steel (SCM440)
Material	SUS304 (18-8)	SCM440 (42CrMo4)
Tensile strength	Min. 700 MPa	Min. 1,220 MPa
Corrosion resistance	Excellent	Moderate (black oxide)
Surface	Passivated (natural silver)	Black oxide
Non-magnetic	Yes (generally)	No
Food / medical safe	Yes	No
Best for	Food, medical, outdoor, corrosion-sensitive pivots	High-load dynamic, robotics, automotive

Shoulder Diameter to Thread Size Relationship (ISO 7379)

Shoulder Dia. (d1)	Thread Size (d2)	Head Dia. (d3)	Head Height (l2)	Key Size (s)	Key Depth (t)
φ 5 mm	M4	8.0	4.5	3	2.0
φ 6 mm	M5	10.0	5.5	4	2.5
φ 8 mm	M6	13.0	7.0	5	3.0
φ 10 mm	M8	16.0	8.5	6	4.0
φ 12 mm	M10	18.0	10.0	8	4.5
φ 16 mm	M12	24.0	13.0	10	5.5
φ 20 mm	M16	30.0	16.0	14	7.0

Shoulder Tolerance — h6 Precision Ground

The shoulder diameter is precision-ground to h6 tolerance per ISO 286-1. This is a close-clearance fit tolerance suitable for rotating and sliding applications:

Shoulder Dia.	h6 Upper Deviation	h6 Lower Deviation	h6 Tolerance Band
φ 5 mm	0	−8 μm	8 μm
φ 6 mm	0	−9 μm	9 μm
φ 8 mm	0	−15 μm	15 μm
φ 10 mm	0	−15 μm	15 μm
φ 12 mm	0	−18 μm	18 μm
φ 16 mm	0	−18 μm	18 μm
φ 20 mm	0	−21 μm	21 μm

For rotating applications (bearings, bushings): pair with H7 bore tolerance for a standard clearance fit (H7/h6). For sliding/guiding applications: H8 or H9 bore provides more clearance.

Material — A2 Stainless Steel (SUS304) Chemical Composition (%)

All values are maximum unless a range is indicated.

Grade	C (max)	Si (max)	Mn (max)	P (max)	S (max)	Cr	Ni
SUS304 (A2)	≤0.08	≤1.00	≤2.00	≤0.045	≤0.030	18.00–20.00	8.00–10.50

Mechanical Properties — A2-70 (ISO 3506-1)

Property	Requirement	Unit
Tensile Strength (Rm)	Min. 700	MPa
Proof Load Stress (Rp0.2)	Min. 450	MPa
Hardness (max)	≤95 HRB / ≤210 HV	HRB / HV
Elongation after fracture (A)	Min. 25	%
Shoulder Tolerance	h6 (precision ground)	—
Surface Treatment	Passivation (natural finish)	—

Key Features

• Precision h6 shoulder — ground to h6 tolerance for accurate pivot, guide, and bearing applications
• A2 Stainless Steel (SUS304) — excellent corrosion resistance in atmospheric, freshwater, food processing, and mild chemical environments
• Passivated natural finish — clean silver appearance with enhanced oxide layer for superior rust resistance
• Reduced thread diameter — thread is always smaller than shoulder, ensuring the shoulder bears the load
• Non-magnetic — suitable for applications sensitive to magnetic interference
• Hygienic & food-safe — smooth passivated shoulder compliant for food processing and medical equipment
• RoHS & REACH compliant — no restricted hazardous substances
• ISO 7379 standard — internationally recognized specification for socket head shoulder screws

Corrosion Resistance Guide — A2 (SUS304)

Environment	A2 (SUS304) Performance	Recommendation
Indoor / dry environments	Excellent	✅ Ideal
Outdoor / atmospheric exposure	Very good	✅ Suitable
Food processing / pharmaceutical	Excellent	✅ Ideal
Freshwater / mild humidity	Very good	✅ Suitable
Mild chemical exposure	Good	✅ Generally suitable
Saltwater / marine (direct)	Limited	⚠️ Consider A4 (SUS316)
Strong acids / chlorides	Poor	❌ Not recommended

Applications

FULLERKREG ISO 7379 A2 stainless steel socket head shoulder screws are widely used in corrosion-sensitive precision pivot and guide applications:

• Food processing and packaging machinery — pivot pins and linkage axes requiring corrosion resistance
• Pharmaceutical and medical device manufacturing — precision pivots in hygienic environments
• Outdoor equipment and architectural hardware — hinges and pivot mechanisms exposed to weather
• Laboratory instruments and scientific equipment
• Electronics and semiconductor equipment — non-magnetic pivot requirements
• Marine and coastal equipment — pivot and guide applications in humid environments
• Jigs and fixtures in corrosive environments
• Any precision pivot or guide application requiring corrosion-resistant shoulder screws

How to Specify a Shoulder Screw

When ordering ISO 7379 shoulder screws, specify the following parameters:

• Shoulder diameter (d1) — the functional diameter that mates with your bearing or bushing bore (e.g., φ8 mm)
• Shoulder length (l1) — the length of the smooth shoulder section (e.g., 20 mm)
• Thread size (d2) — determined by shoulder diameter per ISO 7379 table (e.g., M6 for φ8 mm shoulder)

Example specification: ISO 7379 — 8 × 20 — A2-70 (shoulder diameter 8 mm, shoulder length 20 mm, A2-70 stainless)

Frequently Asked Questions

Q: What is the difference between a shoulder screw and a standard socket cap screw?
A standard socket cap screw has a uniform thread along its full body length. A shoulder screw (ISO 7379) has a precision-ground smooth shoulder that is larger in diameter than the thread. The shoulder is the functional element — it acts as a precision shaft for bearings, bushings, and pivots. The thread only provides clamping force.

Q: What bore tolerance should I use with an h6 shoulder screw?
For rotating applications (bearings, bushings): use H7 bore tolerance for a standard clearance fit (H7/h6). For sliding/guiding applications: use H8 or H9 bore for more clearance.

Q: Why choose A2 stainless instead of Grade 12.9 alloy steel for shoulder screws?
If your application involves corrosive environments, food processing, medical equipment, or requires non-magnetic properties, A2 stainless is the correct choice. For high-load dynamic applications requiring maximum strength (1,220 MPa), Grade 12.9 SCM440 is preferred.

Q: Does the passivation treatment affect the h6 shoulder tolerance?
No. Passivation is a chemical surface treatment that removes free iron and enhances the natural oxide layer. It has no measurable effect on shoulder dimensions. The h6 tolerance is maintained after passivation.

Q: Can I get dimensional inspection reports for the shoulder diameter?
Yes. FULLERKREG provides shoulder diameter inspection reports, material certificates, and PPAP documentation upon request.

Packaging & Availability

• Shoulder diameters φ5 – φ20 mm available in multiple shoulder lengths
• Bulk carton packaging; small box and custom packaging available
• Shoulder diameter inspection reports and material certificates available on request
• PPAP report available on request
• Custom shoulder lengths accepted for large orders

Download Specification

• ISO 7379 — Full Dimensional Specification (PDF)

Quality Assurance

All FULLERKREG ISO 7379 A2 stainless steel socket head shoulder screws are manufactured under strict quality control procedures including:

• Shoulder diameter inspection (h6 tolerance verification)
• Hardness test (≤95 HRB)
• Tensile strength test (min. 700 MPa)
• Surface roughness inspection (shoulder ground finish)
• Dimensional inspection per ISO 7379
• Chemical composition verification (SUS304)
• PPAP documentation available upon request

For wholesale pricing, bulk orders, custom shoulder lengths, or technical inquiries, please contact our sales team.