Precision Fastening for Pivots, Guides & Machinery
A conventional bolt can clamp two components together, but some mechanisms need the fastener itself to become part of the movement. Bremick Socket Head Shoulder Screws combine an internal hex drive, accurately defined unthreaded shoulder & smaller threaded section for machinery, tooling, jigs, fixtures, pivots, guides & industrial assemblies where the shoulder performs a mechanical function.
Often referred to as socket shoulder screws, shoulder bolts or stripper bolts, these specialised fasteners can provide a controlled surface for components to rotate, slide, locate or pivot around. Bremick's metric family includes ISO 7379 Class 12.9 socket head shoulder screws, while an Imperial UNC shoulder screw range provides options for compatible imperial machinery & equipment.
Comparing conventional internal-hex fasteners? Bremick Socket Head Cap Screws covers cap screws designed primarily for clamped assemblies, while Specialty Fasteners provides additional hardware for specialised machinery & engineering applications.
Before replacing a shoulder screw, measure more than the thread. Shoulder diameter, shoulder length, thread diameter, pitch, thread system, head dimensions & available movement clearance can all determine whether the replacement actually belongs in the mechanism.
What Are Bremick Socket Head Shoulder Screws?
Three distinct sections give a shoulder screw its mechanical identity.
A typical socket head shoulder screw includes:
► An internal-hex socket head
► A larger-diameter precision shoulder
► A smaller-diameter threaded section
That stepped geometry separates it from an ordinary socket head cap screw.
The shoulder can act as a locating surface, pivot, spacer, guide or bearing surface while the smaller threaded section retains the fastener in the assembly.
Bremick's metric range demonstrates this clearly:
► 6mm shoulder with M5 thread
► 8mm shoulder with M6 thread
► 10mm shoulder with M8 thread
► 12mm shoulder with M10 thread
► Larger shoulder sizes across the broader range
The important buying rule is simple:
Measure the shoulder first, then confirm the thread.
Ordering solely from the thread size can leave you with a screw that threads into the machine but doesn't fit the component riding on its shoulder.
Why Choose Bremick Socket Shoulder Screws?
The Shoulder Becomes Part of the Mechanism
A normal bolt shank is often little more than the section between head & thread.
A shoulder screw is different.
Its unthreaded shoulder can deliberately interact with another component, providing a defined surface around which that component moves, locates or bears.
That makes dimensional accuracy particularly important.
Useful Where Components Need to Pivot
Levers, linkages & articulated mechanisms need an axis.
Where the assembly is designed around a shoulder fastener, the smooth shoulder can provide that pivot surface while the reduced thread anchors the screw into the surrounding structure.
Wear should be checked on both the shoulder & mating bore during maintenance.
Guide Sliding Components
Some fixtures need controlled linear movement rather than rotation.
A shoulder can guide a component along a slot or bore while limiting unwanted movement elsewhere in the mechanism.
That makes shoulder diameter & clearance just as important as thread selection.
Locate Parts Repeatably
Jigs, fixtures & machine tooling often depend on components returning to predictable positions.
A correctly specified shoulder screw can contribute to repeatable location while also retaining the assembly.
Internal Hex Access Keeps the Head Compact
Machinery rarely offers generous spanner clearance.
The internal hex drive allows installation from directly above the screw head using a correctly sized Allen key, hex key or socket bit.
Good tool fit is essential, particularly when high-strength fasteners are involved.
Common Applications
Machinery Pivots
Picture a lever rotating around a fixed fastener.
If the mechanism is designed around a shoulder screw, the moving component rides on the shoulder rather than directly on the thread.
That creates a cleaner mechanical interface than allowing the component to work across threaded geometry.
Jigs & Fixtures
Repeatability matters when a fixture performs the same operation hundreds of times.
Shoulder screws can provide locating, guiding or pivoting points around clamps, stops & moving fixture components.
A worn shoulder can alter the behaviour of the entire fixture.
Tooling & Dies
The term stripper bolt is often encountered around tooling, moulding & die applications.
Where a shoulder screw performs a specialised movement or guidance function, replace it from the dimensional specification rather than treating it as a generic Allen bolt.
For wider machinery fastening requirements, Bolts & Fasteners provides complementary threaded hardware.
Sliding Mechanisms
Slots, guide plates & moving machine components can rely on a shoulder to control travel.
The surrounding component needs appropriate clearance around the shoulder.
Too much clearance can introduce play.
Too little can create binding.
Machine Building
A purpose-built machine can use shoulder screws in locations where ordinary fasteners wouldn't provide the required mechanical relationship.
Designers & maintenance teams should therefore document shoulder diameter & length, not only thread size.
Manufacturing Equipment
Production machinery turns small dimensional differences into real downtime.
A replacement shoulder screw that's 2mm too long in the shoulder can change component clearance or prevent correct assembly.
Known specifications save time when the machine is already offline.
Mechanical Repairs
A worn shoulder screw often reveals what has been happening inside the mechanism.
Polishing, grooves, scoring, deformation or uneven wear can point to misalignment, contamination or excessive clearance.
Inspect the mating component at the same time.
Agricultural Machinery
Farm equipment can combine metric & imperial fasteners, particularly across machinery from different manufacturers or eras.
Measure rather than guessing from the nearest Allen key.
Workshop Equipment
Presses, drilling fixtures, clamps, adjustment mechanisms & specialised workshop machinery can all contain shoulder screws in locations that aren't obvious until disassembly begins.
Photograph component order before pulling the mechanism apart.
Metric ISO 7379 Shoulder Screws
What Does ISO 7379 Mean?
Technical drawings may call for ISO 7379 shoulder screws rather than using the broader term shoulder bolt.
Bremick's published metric socket screw catalogue identifies its metric coarse shoulder screw family as ISO 7379, Class 12.9, plain finish.
Where ISO 7379 is specified, match the complete fastener geometry rather than simply buying another internal-hex screw.
Important dimensions can include:
► Shoulder diameter
► Shoulder length
► Thread diameter
► Thread pitch
► Head dimensions
► Internal hex size
The standard reference is particularly useful when equipment drawings provide a known specification but the original screw is worn or missing.
Metric Class 12.9 Shoulder Screws
Bremick's metric ISO 7379 range uses Class 12.9 high-strength fasteners.
Published configurations include relationships such as:
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Shoulder Diameter
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Thread
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6mm
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M5
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8mm
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M6
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10mm
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M8
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12mm
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M10
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Multiple shoulder lengths are available across individual diameter families.
Don't interpret Class 12.9 as permission to ignore dimensions.
A high-strength screw with the wrong shoulder is still the wrong component.
Imperial UNC Shoulder Screws
Metric machinery isn't the whole workshop.
Bremick also lists an Imperial UNC Socket Head Shoulder Screw family in plain finish, with the shoulder again larger than the threaded section.
Examples include:
► 1/4 inch shoulder with #10 UNC thread
► 5/16 inch shoulder with 1/4 UNC thread
► 3/8 inch shoulder with 5/16 UNC thread
► 1/2 inch shoulder with 3/8 UNC thread
► 5/8 inch shoulder with 1/2 UNC thread
This stepped relationship is exactly why an imperial shoulder screw shouldn't be identified from its thread alone.
Older machinery, imported equipment & specialised tooling can all make these imperial sizes relevant to Australian maintenance teams.
Product Selection Guide
Measure Shoulder Diameter First
The largest unthreaded section is often the most important dimension.
Shoulder diameter determines how the fastener fits the mating bore or moving component.
If that diameter is incorrect, perfect thread compatibility won't save the assembly.
Use appropriate measuring equipment rather than estimating from the old screw's thread.
Measure Shoulder Length Separately
Shoulder length defines how much usable unthreaded section sits inside the mechanism.
Too short & a moving component may partly bear against the thread.
Too long & the shoulder may prevent the assembly from clamping, seating or travelling correctly.
Record this dimension independently from overall screw length.
Confirm the Reduced Thread
Only after the shoulder has been identified should the smaller thread be confirmed.
Metric shoulder screws may use combinations such as a 10mm shoulder with M8 thread.
Imperial configurations use the same stepped principle.
Don't describe the fastener only as “M8” or “3/8 UNC” when the shoulder dimensions are equally important.
Socket Shoulder Screw vs Socket Head Cap Screw
Their heads can look similar.
Their jobs can be completely different.
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Socket Shoulder Screw
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Socket Head Cap Screw
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Defined precision shoulder
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Conventional shank/thread geometry
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Reduced threaded section
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Thread based around nominal fastener size
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Can act as pivot, guide or locator
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Primarily creates clamping force
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Shoulder diameter & length are critical
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Diameter, thread & length dominate
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Common in mechanisms & fixtures
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Common across broader machinery fastening
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Need conventional cap screws elsewhere on the machine? Screws & Anchors provides a broader threaded-fastener pathway.
Shoulder Screw vs Part-Thread Bolt
An ordinary bolt can contain an unthreaded section.
That alone doesn't make it a shoulder screw.
A purpose-designed shoulder screw uses a defined shoulder diameter & length plus a reduced threaded end.
When the unthreaded section performs a mechanical function, use the specified shoulder fastener rather than improvising with a conventional bolt.
Shoulder Bolt vs Stripper Bolt
Workshop terminology can vary.
Shoulder bolt, shoulder screw & stripper bolt may all appear when researching this fastener family.
The useful ordering information remains:
► Shoulder diameter
► Shoulder length
► Thread diameter
► Thread pitch or system
► Head style
► Material & strength requirements
Names help identify the family.
Dimensions identify the fastener.
Inspect the Mating Bore
A new screw can't restore a worn bore.
Before replacing the fastener, check the component surrounding the shoulder for:
► Ovality
► Scoring
► Burrs
► Corrosion
► Excessive clearance
► Seizure marks
► Uneven wear
If the bore is damaged, replacing only the shoulder screw can leave the underlying mechanical problem unchanged.
Read Wear Marks on the Shoulder
A shiny polished band can be useful evidence.
It identifies where the component has been working against the shoulder.
Deep grooves, stepped wear or discolouration deserve further investigation before a fresh screw goes back into service.
Check the Shoulder-to-Thread Transition
The point where shoulder becomes thread needs sufficient clearance within the assembly.
A moving component shouldn't unintentionally sit across the threaded transition unless the design specifically allows it.
Compare replacement geometry carefully where tolerances matter.
Add Up the Component Stack
Bushes, spacers, washers & moving components all consume shoulder length.
Lay the mechanism out before ordering when the original specification isn't known.
A small difference in stack height can determine whether the assembled component moves freely or binds.
Use Washers Only Where the Assembly Calls for Them
A washer can alter the relationship between the screw head, shoulder & surrounding components.
Don't add one casually to correct a dimensional mismatch.
Where washers are specified elsewhere in the assembly, Flat Washer covers related fastening hardware.
Match the Internal Hex Drive
Internal sockets can be damaged surprisingly quickly by the wrong tool.
Use the correct metric or imperial hex key or drive bit & engage it fully.
For related installation accessories, Hex Drive Bits & Inserts provides compatible internal-hex tooling.
Avoid Ball-End Keys for Heavy Final Tightening
Ball-end Allen keys are excellent for angled access.
Their reduced contact area makes them less suitable for demanding final tightening.
Where higher tightening load is required, use suitable straight engagement.
Watch for Bottoming in Blind Holes
A screw can feel tight without securing the assembly.
If the threaded section reaches the bottom of a blind hole before the shoulder seats correctly, additional tightening only increases the risk of damage.
Confirm usable thread depth before fitting a longer replacement.
Don't Accidentally Clamp a Moving Component
A shoulder screw may deliberately allow another component to rotate or slide.
Changing shoulder length, spacer thickness or washer arrangement can unintentionally clamp that component between surfaces.
Check freedom of movement after reassembly where movement is part of the design.
Tightening Comes From the Assembly Specification
Shoulder diameter isn't a torque value.
Thread size, material, fastener strength, lubrication, joint design & equipment requirements all influence tightening.
Where the machine manufacturer or engineering documentation provides a tightening requirement, use it.
Keep Imperial & Metric Hardware Separate
An almost-right shoulder screw is rarely useful.
Clearly separate:
► Metric ISO 7379 shoulder screws
► Imperial UNC shoulder screws
► Conventional socket cap screws
► Other internal-hex fasteners
Good storage prevents rushed substitutions during breakdowns.
Record the Machine Location
For frequently serviced equipment, add the shoulder screw specification to the maintenance record.
Include:
► Machine
► Assembly location
► Shoulder diameter
► Shoulder length
► Thread specification
► Fastener family
That turns the next replacement into a parts lookup rather than another measuring exercise.
For complementary nuts & conventional threaded hardware used elsewhere on machinery, Nuts & Washers provides related fastening components.
Expert Tips for Shoulder Screw Selection
Thread fits but the mechanism has play? Measure the shoulder diameter before blaming the bore.
Moving part binds after replacement? Compare shoulder length, spacers & component stack against the original assembly.
Old shoulder has one heavily polished side? Check alignment & mating-bore wear rather than treating it as ordinary cosmetic wear.
Drawing specifies ISO 7379? Match the full metric shoulder screw geometry, not simply the thread.
Imperial machine has a missing screw? Confirm fractional shoulder size & UNC thread before trying the nearest metric replacement.
Allen recess already rounded? Replace questionable hardware while access is good instead of reinstalling a future extraction job.
Fastener bottoms before the head reaches position? Check blind-hole depth before adding torque.
Pivot remains sloppy with a new shoulder screw? Inspect the bush or mating bore for wear.
Fixture repeatedly damages the same fastener? Investigate loading, alignment & component movement rather than assuming the screw is the sole problem.
A small fastener can carry an important mechanical role inside expensive equipment. Why Good Fasteners Matter More Than the Tool You Drive Them With looks at why dependable hardware deserves careful selection.
