Set Screws / Grub Screws (Socket Set Screws, Headless Screws)
In rotating assemblies, the failure is rarely “the screw breaks.” The more common problem is slip on the shaft, caused by inadequate holding torque, surface hardness mismatch, or the wrong point geometry. A set screw (grub screw) solves a very specific engineering task: it creates a controlled contact point that locks a hub component—gear fixing, pulley fastener, shaft collar screw—without adding external protrusions.
Where projects lose time is during service: stripped internal hex, galling in stainless threads, or a cup point that chews the shaft and still loosens under vibration. We manufacture hex socket / internal hex (Allen drive) set screws to DIN 916 / ISO 4029 (cup point) and supply other point types—flat point, cone point, dog point, knurled cup point—so you can match the screw to the shaft material, torque strategy, and rework expectations.
- Lock hubs without protruding head
- Choose cup/flat/cone/dog points
- Allen drive supports compact access
- Offer knurled cup anti-walk option
- Supply A2/A4 stainless grades
- Control hardness; reduce stripping
Technical Specifications
Product Name
Set Screws / Grub Screws / Socket Set Screws / Headless Screws (Blind Screws)
Standards
DIN 916 / ISO 4029 (hex socket, cup point); related options: DIN 913 (flat), DIN 914 (cone), DIN 915 (dog) available on request
Material
Stainless steel 304 (A2), 316 (A4); Alloy steel (e.g., SCM435 / 42CrMo for Q&T); Carbon steel (project-dependent)
Grades
Stainless: A2-70 / A4-70 / A4-80 (when specified); Alloy steel: property class per drawing (common high-strength selections available)
Thread Type
Metric coarse (ISO 724), fine thread on request; UNC/UNF for imperial
Diameter Range
Metric: M3–M12 common (M3/M4/M5/M6/M8 typical); Imperial sizes available on request
Surface Finish
Stainless passivated; Black oxide (indoor); Zinc plated (Cr3); Zinc-Nickel; Flake coatings (Geomet/Dacromet) for corrosion programmes
Certifications
ISO 9001:2015, EN 10204 3.1 material certificates, RoHS/REACH declarations on request; PPAP/traceability available
1: Shaft slip after assembly (insufficient holding / wrong point type).
What happens in real use: A door handle screw or small pulley fastener feels tight at install, then backs off after vibration or thermal cycling. The root cause is usually contact mechanics: too little bite, or the wrong point for the shaft hardness/finish.
Engineering match:
Cup point (DIN 916 / ISO 4029): good general-purpose bite on shafts and collars; creates a circular indentation for holding torque.
Flat point: for delicate shafts or when you must avoid shaft damage; relies more on friction than penetration.
Cone point: high penetration and holding on softer shafts; higher risk of shaft scoring.
Dog point: locates into a drilled/reamed recess for repeatable positioning; reduces lateral walking if the recess is designed correctly.
Knurled cup point: increases resistance to loosening in vibration, at the cost of more shaft marking.
2: Stripped drive during tightening (internal hex rounding).
What happens on the floor: Small sizes (M3–M5) are sensitive to tool wear and misalignment. Once the hex socket / Allen drive rounds, extraction time dominates.
Solution: control drive depth and hardness, use correct key size, and specify torque limits consistent with screw size and lubrication state.
3: Galling and seizure (stainless on stainless).
What happens in service: A2/A4 stainless set screws can gall in stainless tapped holes, especially under high contact pressure and dry assembly.
Solution: define lubrication/anti-seize policy, consider dissimilar pairing (stainless screw into plated steel insert), and avoid over-torque.
4: Micro-motion and fretting (preload decay in vibrating hubs).
What happens in rotating machinery: Small slip events create fretting debris; holding torque drops further.
Solution: combine correct point type + surface prep, and add threadlocking where validation requires (patch, liquid threadlocker, or prevailing torque feature in the joint design).
Example table for “set screw dimensions / grub screw dimensions” searches. Confirm against the specified standard edition and tolerances for release.
| Thread d | Pitch P (coarse) | Hex socket s (Allen) | Length l (example) | Point type | Typical applications |
|---|---|---|---|---|---|
| M3 | 0.5 | 1.5 | 3–8 mm | Cup point | 3D printer parts, small hubs |
| M4 | 0.7 | 2.0 | 4–12 mm | Cup point | Door handle screw, fixtures |
| M5 | 0.8 | 2.5 | 5–16 mm | Cup point | RC car parts, collars |
| M6 | 1.0 | 3.0 | 6–20 mm | Cup point | Shaft collar screw, gears |
| M8 | 1.25 | 4.0 | 8–25 mm | Cup point | Pulley fastener, machinery |
| M10 | 1.5 | 5.0 | 10–30 mm | Cup point | Larger hubs, industrial hardware |
Dimension notes engineers verify
s (internal hex) drives tool selection and strip risk.
l must deliver full thread engagement without bottoming.
For dog point, define dog length and recess geometry on the mating part.
Achieve reliable holding without stripping drives, damaging shafts unnecessarily, or creating galling failures.
Torque, contact, and “holding” reality
A set screw’s function is contact locking, not bolt-style preload clamping. Over-torquing mainly increases shaft damage and drive stripping risk.
Use size-appropriate torque drivers for M3–M6 where variability is high.
Lubrication policy (especially stainless)
Stainless A2/A4: manage galling with defined lubrication/anti-seize. Dry stainless-on-stainless is a common seizure mode.
Plated/alloy steel: lubrication changes friction and can increase achieved clamp/contact for the same torque—do not mix “dry” and “oiled” assembly specs.
Thread engagement and bottoming check
Ensure adequate thread engagement in the tapped hole; avoid bottoming (false torque). A bottomed set screw feels “tight” but delivers poor holding.
For blind holes, specify a controlled minor depth so the cup point can seat properly.
Washers (when applicable)
Set screws typically do not use washers; however in some assemblies (e.g., thin-walled hubs) a hardened insert pad or thrust pad can prevent thread distortion and improve repeatability.
Hole clearance and access (ISO 273 reference)
ISO 273 is relevant when the set screw is accessed through a clearance hole in a guard, collar, or housing. Use an appropriate ISO 273 clearance series so tools can align fully with the socket—misalignment is a frequent cause of rounded internal hex drives.
Anti-loosening options
For vibration: consider pre-applied patch, liquid threadlocker, or knurled cup point depending on whether shaft marking is acceptable. Validate by test (service vibration profile), not assumption.
Related Products
FAQ
What is a set screw (grub screw) used for?
A set screw is used to lock a hub component to a shaft without a protruding head. It is common in shaft collars, gear fixing, pulleys, and door handle assemblies.
What standard covers cup point socket set screws?
DIN 916 and ISO 4029 cover hex socket cup point set screws. If you need flat, cone, or dog point versions, specify the corresponding standard or point type on the drawing.
Cup point vs flat point—what should I choose?
Cup point provides higher holding by biting into the shaft, while flat point reduces shaft damage but relies more on friction. The correct choice depends on shaft hardness, surface finish, and whether shaft marking is acceptable.
Why does a stainless set screw seize or gall?
Stainless set screws can gall when stainless threads rub under high pressure, especially when assembled dry. Use a defined lubrication/anti-seize policy and avoid over-torque to reduce seizure risk.
How do I stop a set screw loosening under vibration?
Use the correct point type, ensure proper seating (no bottoming), and add a locking method such as a pre-applied patch or threadlocker. For high vibration where shaft marking is acceptable, a knurled cup point can increase resistance to backing out.