Grub Screw Sizes Selection Guide | Hebei Wotu Fastener Manufacturing Co., Ltd.
Grub screw sizes determine whether a headless screw will engage the internal thread correctly and seat against the mating part without protruding. Start with the thread diameter, thread pitch, and length; then match the point style and drive to the shaft, hub, collar, or other assembly.
A designation such as M4 × 6 generally refers to a 4 mm nominal thread diameter and a 6 mm nominal length, but the required size also depends on the available threaded hole depth and how much engagement the assembly needs.
Brand: Hengzuan Surface: blue and white zinc plated Specifications: in stock ST2.9/ST3.5/ST4.2/ST4.8/ST5.5 Chinese national standard full series, complete rod length 13~60mm, supports nonstandard length customization; drilling adapts to steel sheet thickness 2~6mm Packaging: 25kg cartons, whole wooden pallets
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Brand: Wotu Surface: Natural black oxide treatment, customized hot-dip galvanized, zinc plated as required Specifications: Follow Chinese national standard GB/T799-1988, in stock M12-M48, total length 120mm~1500mm, nonstandard customized diameter, bending length, total screw length available Matching: Nuts, flat washers and spring washers of the same specification can be supplied in complete sets. Packaging: Bundling and packaging, using wooden pallets and film-wrapped export packaging in large quantities
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Brand: Hengzuan Surface: Color zinc plated, optional blue-white zinc plated, black oxide treatment Specifications: Chinese national standard ST4.2/ST4.8/ST5.5 specifications, rod length 13~50mm in stock, supports nonstandard length customization Packaging: 25kg export cartons, full wooden pallets wrapped with film, supports neutral packaging, private-label customization
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Brand: Hengzuan Surface: blue and white zinc plated, can be customized color zinc plated, black oxide plated Specifications: Comply with GB/T15856.2-2002 Chinese national standard, in stock ST4.2/ST4.8/ST5.5 full range of specifications, length 13mm~75mm optional, supports customized nonstandard rod lengths; drilling adaptation plate thickness 0.7~6mm Packaging: 25kg export cartons, full pallets wrapped with film, supports neutral export packaging, customer private-label customization
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Brand: Hengzuan Surface: blue and white zinc plated, can be customized color zinc plated, black oxide plated Specifications: in stock 3.5/3.9/4.2/4.8/5.5 mainstream wire diameter, rod length 13mm~75mm full size range, nonstandard length can be customized as needed Packaging: 25kg export cartons, full wooden pallets wrapped with film, supports neutral export packaging, private-label customization
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Brand: Hengzuan Surface: color zinc plated, customized blue-white zinc plated, black oxide Specifications: in stock 3.9/4.2/4.8/5.5 full diameter, length 13mm~75mm full size range, supports customized nonstandard rod lengths Packaging: 25kg export cartons, full pallets wrapped with film, supports neutral export packaging, customer private-label customization
Read MoreGrub screw size considerations
Compare grub screws by thread diameter and pitch, nominal length, point form, drive size, material, finish, and compatibility with the mating part. The correct choice is the one that fits the tapped hole, reaches the intended contact surface, and can be installed without damaging nearby components.
| Criterion | What To Check | Why It Matters | Buyer Tip |
|---|---|---|---|
| Nominal diameter and thread pitch | Match the screw diameter and pitch to the tapped hole or mating thread using a thread gauge or engineering drawing. | A diameter or pitch mismatch can prevent assembly or damage the internal thread. | Ask: Can you supply the required thread designation, pitch, and a sample for fit verification? |
| Screw length | Measure a grub screw from its end to end and compare that length with the available threaded depth and engagement requirement. | An undersized screw may not hold securely, while an oversized screw can protrude into moving or mating parts. | Ask: Should the specified length provide full engagement without reaching beyond the component? |
| Point style | Compare the required point—flat, cup, cone, dog, or another form—with the contact surface and holding method. | The point changes how the screw contacts the shaft or component and can affect grip, marking, and removal. | Ask: Which point style suits the contact surface, and is a drawing or sample available for confirmation? |
| Drive type and socket size | Confirm the internal drive form and the tool size available for installation in the final assembly. | The drive must transmit installation torque without tool interference or socket damage. | Ask: What drive and key size will be supplied for the selected diameter and length? |
| Material and surface finish | Review the base material and finish against load, exposure, corrosion concerns, and contact with other metals. | Material and finish affect durability, corrosion resistance, and the risk of damaging the mating component. | Ask: Which material and finish are available for the service environment, and what documentation accompanies them? |
The thread size and the screw length solve different fit problems. The diameter and pitch must match the tapped hole, while the length determines thread engagement and how far the screw reaches into the mating component. Choosing a longer screw is not automatically better: it may bottom out, interfere with internal parts, or extend beyond the assembly.
Point style matters as well. A flat point suits a prepared contact surface, while cup, cone, or another point form may provide a different grip or contact pattern. Confirm the point geometry and internal drive type rather than ordering by diameter and length alone.
Match the thread system first. Specify metric or inch threads, nominal diameter, and pitch. A similar-looking diameter with a different pitch will not provide a correct fit. If the existing tapped hole is uncertain, check the mating component drawing or identify the thread with a suitable gauge before requesting a quotation.
Choose length from the assembly, not from the screw alone. Account for the depth of the tapped hole, the thickness of the part being secured, and the contact point on the shaft. Avoid bottoming the screw before it clamps, leaving too little engagement, or selecting a length that intrudes into moving or sensitive components.
Select the point and drive for the application. A cup point can suit general holding on a shaft, while a flat or cone point may be preferable where contact damage, alignment, or a defined seating mark matters. An internal hex or other drive should also match the available installation tool and the access around the fastener.
Prevent specification errors at the enquiry stage. Send the thread designation, length, point style, drive type, material or finish requirement, and a simple drawing or photograph of the mating hole if available. Ask the supplier to confirm how length is measured, the applicable thread standard, and whether the proposed point geometry matches the contact surface.
| Criteria | Importance | Description | Example Options |
|---|---|---|---|
| Thread diameter and pitch | Critical for fit | The external thread must match the tapped hole exactly. A correct diameter with the wrong pitch can bind, strip the thread, or fail to seat. | An M6 grub screw must be matched with the correct M6 pitch specified on the mating component drawing. |
| Screw length | Critical for engagement and clearance | Length controls how much thread engages and where the point contacts the mating part. Too short may not hold; too long may bottom out or interfere with nearby parts. | A blind tapped hole needs enough clearance so the screw tightens against the shaft rather than the bottom of the hole. |
| Point style | Application-dependent | The point determines the contact pattern and holding behaviour. Cup, flat, cone, and other point forms can suit different surfaces and marking requirements. | A flat point may be preferred where a shaft surface should not be heavily indented. |
| Drive type and access | Important for installation | The internal drive must match the available tool and the space around the fastener. Poor tool access can lead to incomplete tightening or damaged sockets. | An internal hex drive may be practical in a recessed collar if there is enough clearance for the hex key. |
| Material and finish | Depends on the working environment | Material and surface finish affect corrosion resistance, strength, appearance, and compatibility with the assembly. These should be selected after the size and geometry are confirmed. | A fastener used in a dry indoor mechanism may have different finish requirements from one exposed to moisture. |
Related Options
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In a metric designation, M5 is the nominal thread diameter and 8 is the nominal screw length in millimetres. You should still confirm the thread pitch, because fine and coarse pitches can share the same nominal diameter but will not fit the same tapped hole.
Not always. A longer screw may give more thread engagement, but it can bottom out in a blind hole, protrude into the assembly, or reach a surface it should not contact. Choose the length from the tapped-hole depth and the required contact position, not from diameter alone.
A cup point is often used where the screw needs to bite into a shaft or similar surface for holding force. A flat point spreads contact more gently on a prepared surface, while a cone point creates a more concentrated seating mark. The best choice depends on whether grip, repeatable positioning, or reduced surface marking matters most.
You should not assume interchangeability. Metric and inch threads use different diameter and pitch systems, and a close visual match can still damage the internal thread or fail to tighten properly. Confirm the original thread standard before selecting a replacement.
Send the thread system, nominal diameter, pitch, length, point style, drive type, material or finish requirement, and quantity. If the screw fits an existing part, include the tapped-hole depth or a drawing so the supplier can check whether the requested length and point style are suitable.
Please provide the required thread standard and size, screw length, and point or drive style. If possible, include the tapped-hole dimensions and the application or mating part so the fit can be reviewed.
