337/338 Series Self-Tapping Inserts are an alternative blind-hole version of the 307/308 series. These inserts feature a chip-reservoir cutting slot and are designed to create durable internal threads in light metals, plastics, and other low-strength base materials without the need for pre-tapping.
During installation, the insert cuts its own mating thread as it is driven into the pre-drilled hole. The integrated chip-reservoir slot captures and retains the generated cutting chips, significantly reducing the risk of debris falling into sensitive internal components. This design improves installation reliability and makes the 337/338 series especially suitable for blind-hole applications where chip control is critical.
Product Structure
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Category |
3-Hole Self-Tapping Insert – Short |
3-Hole Self-Tapping Insert – Long |
3-Hole Semi-Closed Self-Tapping Insert – Short |
3-Hole Semi-Closed Self-Tapping Insert – Long |
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3D Drawing |
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Cutting Design |
Three cutting holes (120° evenly spaced) |
Three cutting holes (120° evenly spaced) |
Three cutting holes + semi-closed bottom |
Three cutting holes + semi-closed bottom |
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Bottom Structure |
Open bottom |
Open bottom |
Semi-closed bottom (chip-blocking) |
Semi-closed bottom (chip-blocking) |
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Effective Thread Engagement |
Medium |
High |
Medium |
High |
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Recommended Hole Type |
Blind hole / Through hole |
Blind hole / Through hole |
Blind hole (preferred) |
Blind hole (preferred) |
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Pre-Drilling Requirement |
Drilling only (no pre-tapping) |
Drilling only (no pre-tapping) |
Drilling only (no pre-tapping) |
Drilling only (no pre-tapping) |
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Reference Drill Diameter |
Slightly smaller than insert OD (per size) |
Same as short version |
Same as open-bottom version |
Same as open-bottom version |
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Minimum Blind Hole Depth |
L + 1–2 mm clearance |
L + 1–2 mm clearance |
Precisely controlled to match semi-closed bottom |
Precisely controlled to match semi-closed bottom |
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Typical Materials |
Carbon steel / Stainless steel |
Carbon steel / Stainless steel |
Carbon steel / Stainless steel |
Carbon steel / Stainless steel |
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Surface Treatment (Optional) |
Zinc plated, passivated, etc. |
Zinc plated, passivated, etc. |
Zinc plated, passivated, etc. |
Zinc plated, passivated, etc. |
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Design Limitations |
Lower load vs long version |
Requires deeper hole |
Requires precise hole depth |
Requires precise hole depth |
Related Products
Compared with 307/308 Type Self-Tapping Inserts
Blind hole self-tapping inserts and standard self-tapping inserts are both designed to create durable, load-bearing internal threads in softer base materials such as aluminum alloys, magnesium alloys, and engineering plastics.
By cutting or forming their own mating threads during installation, they significantly improve thread strength, wear resistance, and service life compared with directly tapped threads.
Although both insert types operate on the same self-tapping principle, their structural design and chip-handling method differ, leading to distinct advantages depending on hole type, installation conditions, and application requirements.
Installation and Machining Characteristics
Blind hole self-tapping inserts require more precise control of pilot hole depth to ensure adequate chip storage volume. However, this design greatly reduces the risk of penetrating the bottom surface of the component.
Standard self-tapping inserts offer greater machining tolerance and easier installation, especially in high-volume production environments. Their open design allows faster chip evacuation and generally higher installation efficiency.
Performance Considerations
From a mechanical standpoint, both insert types provide comparable thread strength and load-carrying capacity when manufactured from the same material and installed correctly.
Blind hole self-tapping inserts offer advantages where:
- Chip containment is critical
- The hole bottom must remain intact
- A clean external appearance or sealing surface is required
Standard self-tapping inserts are often preferred where:
- Through holes are used
- Manufacturing simplicity and cost efficiency are priorities
- No restrictions exist at the hole exit
Metric Series Specifications
337 Series
|
Internal Thread |
External Thread |
Length |
Recommended Tap Drill T |
Minimum Hole Depth L |
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Aluminum |
Iron Steel |
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M3 |
M5-0.6 |
4 |
4.6-4.7 |
4.7-4.8 |
6 |
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M3.5 |
M6-0.8 |
5 |
5.5-5.6 |
5.6-5.7 |
7 |
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M4 |
M6.5-0.8 |
6 |
6.0-6.1 |
6.1-6.2 |
8 |
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M5 |
M8-1 |
7 |
7.4-7.6 |
7.6-7.7 |
9 |
|
M6 |
M10-1.25 |
8 |
9.3-9.5 |
9.5-9.6 |
10 |
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M8 |
M12-1.5 |
9 |
11.1-11.3 |
11.3-11.5 |
11 |
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M10 |
M14-1.5 |
10 |
13.1-13.3 |
13.4-15.4 |
13 |
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M12 |
M16-1.75 |
12 |
15.0-15.2 |
15.2-15.4 |
15 |
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M14 |
M18-2 |
14 |
17.0-17.2 |
17.2-17.4 |
17 |
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M16 |
M20-2 |
14 |
19.0-19.2 |
19.2-19.4 |
17 |
338 Series
|
Internal Thread |
External Thread |
Length |
Recommended Tap Drill T |
Minimum Hole Depth L |
|
|
Aluminum |
Iron Steel |
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M3 |
M5-0.6 |
6 |
4.6-4.7 |
4.7-4.8 |
8 |
|
M3.5 |
M6-0.8 |
8 |
5.5-5.6 |
5.6-5.7 |
10 |
|
M4 |
M6.5-0.8 |
8 |
6.0-6.1 |
6.1-6.2 |
10 |
|
M5 |
M8-1 |
10 |
7.4-7.6 |
7.6-7.7 |
13 |
|
M6 |
M10-1.25 |
12 |
9.3-9.5 |
9.5-9.6 |
15 |
|
M8 |
M12-1.5 |
14 |
11.1-11.3 |
11.3-11.5 |
17 |
|
M10 |
M14-1.5 |
18 |
13.1-13.3 |
13.4-15.4 |
22 |
|
M12 |
M16-1.75 |
22 |
15.0-15.2 |
15.2-15.4 |
26 |
|
M14 |
M18-2 |
24 |
17.0-17.2 |
17.2-17.4 |
28 |
|
M16 |
M20-2 |
24 |
19.0-19.2 |
19.2-19.4 |
28 |
Typical Application Areas
Modern industrial products and equipment require reliable and high-performance fastening solutions to meet increasingly complex structural demands. Many critical components need secure connections, and Nexlok Industrial applies its expertise to deliver these connections, allowing our customers to focus on the functionality of their products. We cover almost every fastening area-whether in from machinery to structural components. Whatever the application, Nexlok Industrial provides self-tapping insert solutions or collaborates with you to develop customized designs.
On the following pages, you can explore the areas where our self-tapping inserts are already successfully applied and discover the innovations we have in store.
STRUCTURAL COMPONENTS AND SUPPORTS
Structural and support components require high-strength fastening and sealing solutions. Our self-tapping inserts ensure that parts are securely attached while maintaining necessary hole sealing and anti-loosening performance, guaranteeing long-term stability.
FLUID AND AIR ROUTING
In fluid and pneumatic systems, self-tapping inserts provide high-strength, safe mounting for clamps, brackets, and tubing connections. With deep customer understanding and technical expertise, Nexlok Industrial is your trusted partner for fluid and air line fastening solutions.
ELECTRIC DRIVE SYSTEMS (EV)
In electric vehicles and electric machinery, self-tapping inserts play a key role in securing drive components. Our innovative solutions not only exceed the standard requirements for electric systems but also improve production efficiency and assembly reliability.
COMBUSTION DRIVE SYSTEMS (ICE)
For traditional combustion engine equipment, self-tapping inserts provide reliable fastening for transmission mounts, engine brackets, wheel hubs, and chassis components. Nexlok Industrial's extensive knowledge and expertise ensure every critical component is securely connected.
How to Install Self Tapping Inserts?
Installation Procedure
● Drill the hole to the specified diameter and countersink where required.
● Fit the self tapping inserts onto the installation tool with the cutting slot or cutting holes facing downward.
● Ensure the driving stud engages no more than half the height of the cutting slot or hole.
● Keep the installation tool and insert aligned perpendicular to the hole throughout insertion.
● When using a production driver, position the rotating sleeve against the exposed stop pins so it is driven clockwise.
● Set the depth stop, where applicable, to seat the insert 0.1–0.2 mm below the surface of the base material.
● Apply consistent downward pressure while driving the self tapping inserts to the required depth.
● Reverse the tool to disengage it from the insert; production drivers release automatically, while hand tools require the hex nut to be held during reversal.
● Avoid bottoming the insert or applying excessive torque, as this may damage the threads or reduce pull-out performance.
Notes
● Most insertion issues result from incorrect hole sizing, poor tool condition, or improper installation technique.
● Trial installations are strongly recommended before starting production.
Delivery & Service | Nexlok Industrial
Standard Delivery for Stock Products
For products available in our inventory, we ensure same-day dispatch. Depending on your location and chosen logistics method, delivery typically takes 5–10 business days.
01
Custom Production & Orders
For customized Loctite-Coated Inserts or non-standard specifications, our production lead time is approximately two weeks after order confirmation. We provide end-to-end support, from material selection and thread design to coating application and quality control.
02
Quality Assurance & Testing
All inserts undergo strict inspection and testing, including pull-out strength, torque resistance, and coating adhesion tests, ensuring that every piece meets industrial standards. Suggested image: Photo of lab equipment testing inserts, e.g., torque tester, pull-out test rig, or QC team inspecting products.
03
How to Order
● Select the product: Browse our catalog or contact us with your specifications.
● Confirm requirements: Quantity, thread size, coating type, and delivery date.
● Place your order: Our professional sales team will confirm lead times and shipping options.
04
Contact Us
For inquiries about Loctite-Coated Thread Inserts, pricing, or technical consultation, our team is ready to respond within 2 hours.
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