We manufacture custom brass threaded inserts for OEM plastic injection molded parts, produced strictly to customer drawings with defined thread standards, controlled OD, and specified knurl geometry. We cut them to perfect fit that hold, moves, flexes, and shrinks over time. Every batch we dispatch goes to through tight quality checks, quality thread gauge inspections, and real press-fit logic.
Heat-set insert for Nylon. Flanged press-in insert for glass-filled PC. We manufacture both types as required by the application. In a recent M8 batch, the insert showed low retention during field installation. We modified the knurl geometry and produced 15 pilot pieces for validation. After confirming improved grip, the change was implemented in production.
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A brass threaded insert is a small metal component placed inside a plastic part to create a strong internal thread.
It replaces weak plastic threads that can strip when a screw is tightened. The insert is locked into the plastic by press-fit, heat-set, mold-in, and ultrasonic installation. This allows screws to be installed, removed, and reinstalled many times without damaging the plastic.
For a broader overview of brass inserts for plastic injection molding, see our main brass inserts page.
Brass straight-knurled insert designed for press-in mounting in plastic housings and injection-molded components.
Brass diamond-knurled insert designed for press-in installation in plastic injection molding.
Brass diamond-knurled insert designed for heat-set installation in injection-molded and 3D-printed plastic parts, electronics assemblies, and industrial plastic components.
Brass diamond-knurled insert with chamfered thread entry, designed for press-in installation in injection-molded and 3D-printed plastic parts.
Brass threaded insert with angled knurling, designed for heat-set installation in injection-molded plastic part.
Brass threaded insert with internal ISO metric M6 thread and straight knurling, suitable for installation in plastic components.
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Brass threaded insert designed as a blind-type insert, featuring a closed top end, and straight knurled outer surface for secure installation in plastic materials. The insert includes a horizontal slot feature visible on the body, supporting controlled installation and alignment while maintaining strong thread retention.
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CNC Precision machined brass insert body featuring an external 15/32-32 thread, shoulder flange, and a U-slot top design for keyed engagement. The insert includes a through bore with defined thread relief and chamfered entry, produced to drawing dimensions for controlled assembly and secure installation.
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We manufacture multiple brass threaded insert designs based on plastic type, installation method, and retention requirement. Each design type is produced to drawing with controlled OD, thread fit, and knurl geometry
We manufacture all of these above listed. Some batches need OD tolerance maintained down to ±0.05 mm and some need to thread pitch to be looked within class 2B. If your part calls for something not off the shelf, we can do it.
We manufacture brass threaded inserts in both Metric and Imperial thread systems because customers use different screw standards.
Metric (ISO) threads are widely used in Europe, much of Asia, and many modern automotive and electronics designs. UNC/UNF threads are still widely used in many legacy industrial and appliance applications in the USA.
We machine both thread systems and follow the fit class written on the customer drawing so the insert works reliably in plastic parts.
| Thread family | Fit class | Typical use | Common sizes |
|---|---|---|---|
| Metric (ISO) | Typical 6H when not otherwise specified | Global OEM products, electronics, and automotive plastics | M2, M3, M4, M5, M6, M8 |
| UNC/UNF (Imperial) | Typical 2B when not otherwise specified | USA legacy assemblies, appliances, and industrial plastics | 2-56, 4-40, 6-32, 10-32, 1/4-20 |
Other fit classes can be machined when they are specified on the drawing. All production threads are checked with Go/No-Go gauges and cleaned before shipment.
In one M5 production batch, plating buildup reduced internal thread clearance. We checked all 2000 pieces with Go/No-Go plug and identified 180 that failed inspection. Those parts were cleaned, re-cut, and rechecked before shipment. This is why our threads fit correctly when they reach the customer’s assembly line.
In real production, five dimensions matter most on a brass threaded insert:outer diameter, overall length, thread depth, entry chamfer, and knurl height.
Customers normally define these on their drawing instead of using standard products. We control each dimension during machining and inspection so the insert installs clean and holds reliably.
| Feature | How we control it | Why it matters |
|---|---|---|
| Outer Diameter (OD) | Machined to a tight tolerance and checked with precision gauges on every batch | Prevents spin-out and avoids cracking thin bosses |
| Overall Length | Cut exactly to the customer drawing | Matches boss depth and prevents bottoming |
| Thread Depth | Controlled in machining and verified with Go/No-Go gauges | Prevents screw bottoming and cross-threading |
| Entry Chamfer | Machined lead-in on every batch | Helps screws start straight and protects threads |
| Knurl Height | Measured and adjusted during production | Too high can crack the boss; too low can cause spin-out |
We treat OD as the main fit dimension, thread depth as the main functional dimension, and knurl height as the main retention control. Every production batch is checked against these three before shipment
Knurl geometry is one of the primary factors affecting how a brass threaded insert grips plastic.
Knurl pattern and height are defined on the approved customer drawing.
If retention adjustments are required after pilot validation, changes are implemented only through formal drawing revision.
Correct knurl geometry allows clean seating, good retention, and protection of thin bosses.
Incorrect knurl design can lead to spin-out even if the thread is correct.
Lower insertion force and smoother press-in feel. Works well when OD tolerance and hole size are consistent. Retention can drop if knurl height is too shallow.
Higher resistance to rotation due to cross-pattern engagement. Provides better anti-rotation in vibration conditions. Requires proper chamfer and taper to avoid installation damage.
Plastics such as ABS and unfilled PA66 may require slightly deeper knurl for proper grip.
Harder plastics such as PC and glass-filled grades require shallower knurl to reduce cracking risk, provided boss wall thickness supports the load.
Heat-set inserts require controlled knurl geometry to allow proper plastic flow during melt installation.
Knurl height is measured during production.
Tooling is adjusted when pilot validation or customer feedback indicates retention issues.
Unlike generic brass inserts , these are all about threads that hold under load, vibration, and torque.
| Insert Type | Install Method | Tools Needed | Strength Profile |
|---|---|---|---|
| Press-In | Manual/Press | Arbor press, jig | High pull-out resistance |
| Heat-Set | Heated tip | Thermal driver | Medium to high, fast fit |
| Self-Tapping | Screw-driven | Driver gun | Quick install, moderate strength |
| Expansion | Threaded bolt expands body | No external press | High lock after set |
Every insert type behaves differently. Press-in inserts need sharp OD knurl and controlled diameter to grip correctly. Heat-set inserts typically use tapered bodies and clean entry chamfers so plastic flows properly during installation. Expansion types use slotted bodies and reamed bores, controlled around ±0.05 mm, so they flex cleanly.
Heat-set insert performance changes with plastic type, boss thickness, boss temperature, and installation tooling. Because of this, there is no single hole size that works for every project. Publishing one fixed number does not reflect real production conditions.
Where possible, we adjust the insert itself so the customer’s mold does not need to change. If the boss design is fundamentally unsuitable, a mold change may still be required. For every new job we control and fine-tune key features:
Where required, vent features are added so softened plastic can flow around the insert instead of trapping pressure.
For first runs we supply pilot inserts made strictly to the approved drawing. The customer installs the samples on their production line. Installation performance depends on their plastic, boss design, and tooling
If the customer later requests a change for easier installation, we review the drawing and adjust features such as OD and knurl only after mutual agreement. Any revision is treated as a formal drawing update before new samples are produced.
Our responsibility is to make inserts accurately to the agreed drawing and maintain the same quality in every batch.
A brass expansion threaded insert is designed to spread outward when a screw is driven in. The body has slots that allow controlled expansion. This expansion presses against the plastic in addition to the knurl grip.
Maker use expansion inserts when normal press-in types do not hold well in a specific plastic design. They work best in softer plastics and thin bosses, provided the boss can tolerate outward pressure. They are useful when customers want mechanical locking without using heat tools.
The insert only locks after the screw is installed. Because of this, expansion inserts handle small hole-size variation better than rigid press-fit types.
We ream the insert bore clean so expansion happens smoothly and repeatably without burr interference.
| Insert type | Install method | Best plastics | Main risk | Typical retention (when design is correct) |
|---|---|---|---|---|
| Press-in | Mechanical press and arbor press | ABS, PC, general rigid plastics | Boss cracking in thin walls | High |
| Heat-set | Heated tip and thermal press | Nylon, PEEK, heat-tolerant plastics | Sink marks, insert float, and uneven temperature | Medium to high |
| Expansion | Screw-driven expansion | Softer plastics & variable holes | Over-expansion from high torque | High after screw is set |
Each method behaves differently. Press-in inserts need sharp, consistent knurl and tight OD control. Heat-set inserts need tapered bodies and clean chamfers for smooth melt flow. Expansion inserts rely on slot design and a smooth internal bore.
Choose the method that matches your plastic, boss design, production speed, and torque requirement.
We cut threads with carbide taps and single point tool. It is depending on thread depth and geometry. After cut:
Some of our flanged closed-end inserts require blind threads controlled to within ±0.10 mm from the base. This is achieved through setup checks, controlled tooling stops, and correctly matched thread relief bores.
We do not ship threads we would not bolt into ourselves.
Threaded inserts fail for predictable reasons. Many production-related failures are caused by tolerance drift, tool wear, and plating variation. We monitor these during production so problems are corrected before shipment.
Knurl height too shallow, OD too small, or plastic mismatch.
We measure OD during the run and verify knurl height. If retention feedback changes, we adjust knurl geometry before the next batch.
Tap wear, chip packing, and material smearing, especially in free-cutting grades such as C36000.
Scheduled tap replacement, air-blast cleaning after cut, and Go/No-Go gauge verification before packing.
Collet drift and OD wear during long production runs..
In-process OD checks with precision gauges. If tolerance shifts, the lot is corrected before dispatch.
Nickel and tin plating adds thickness inside the thread profile.
Controlled pre-plate sizing and gauge inspection after plating to ensure proper fit.
Each batch is verified for thread fit, OD tolerance, and repeatability before shipment.
We manufacture most brass threaded inserts on dedicated automatic insert machines. These machines are designed for high-volume production with stable outer diameter tolerance control, repeatable knurl forming, and integrated tapping stations within the automatic cycle. Standard insert production is not done on general-purpose CNC lathes.
CNC turning is used only for large inserts, special geometries, and when parts requiring tighter features.
Automatic insert machines perform OD turning, knurl forming, facing, and threading in a fixed production sequence. Because each setup is dedicated to one insert type, dimensional consistency remains stable across the batch.
Tool wear is monitored during production. If OD and knurl height begins to shift, tooling is adjusted immediately to maintain tolerance.
Internal threads are produced using integrated tapping stations within the automatic cycle. Tap condition affects pitch accuracy and surface finish, so taps are replaced based on production count, not after failure.
Every batch is verified using calibrated Go/No-Go plug gauges. For plated inserts, threads are checked again after plating to confirm coating thickness has not affected fit.
Specialty inserts are produced on CNC machines using single-point threading to maintain concentricity between thread and outer diameter.
Knurl patterns are formed using dedicated knurling tools to maintain consistent depth and pitch. Knurl height is monitored during production because it directly affects retention.
Shallow knurl reduces grip. Excessive knurl increases installation stress. Tool wear is tracked to prevent profile drift during long runs.
Outer diameter is checked with precision gauges during production. Thread fit is verified before packing. Plated parts receive post-plate inspection to confirm functional engagement.
Machine settings, tooling configuration, and production parameters are recorded for repeat orders. This supports consistent batch performance using the same validated setup.
Threaded inserts are packed according to thread sensitivity and surface finish.
Repeat orders typically ship within 15–20 working days.
New parts requiring tooling or plating may require 20–25 working days
Making one batch right is normal. Making the same part the same way months later is where process control matters. For repeat orders, we do not restart from zero.
We run the same validated setup used on previous production, whether the part runs on automatic insert machines or CNC for special features.
Each insert is produced with assigned tooling. Tool wear history is logged, and cutters are replaced before they affect OD, knurl, or thread quality.
Machine settings, tooling stops, and production parameters are stored for repeat runs. This helps maintain the same dimensions across batches.
The same collets, clamps, and holding methods are used to keep OD, thread pitch, and knurl repeatable.
Go/No-Go gauges are selected according to the customer’s tolerance class when specified.
Sample part photos from inspection are archived to maintain visual and dimensional consistency.
We do not just repeat the drawing. We repeat the manufacturing process.
It depends on plastic type, boss size, hole diameter, boss wall thickness, and installation method. We review your drawing and usually supply pilot inserts for validation before mass production.
Spin-out is normally caused by incorrect hole size, shallow knurl height, and weak plastic material. Retention must be validated in real production, not assumed from catalog data.
Yes. We manufacture non-standard threads for OEM clients across our entire range of Brass Products. We need a clear thread pitch and tolerance zone in the drawing.
Yes. We regularly manufacture closed-end inserts. Short inserts with limited full thread engagement can be manufactured when the drawing supports it. Short-form taps and single-point threading are used to control thread start and finish.
Yes. We supply pilot samples before production tooling is finalized. Mass production begins only after validation.
Threads are checked again after plating. If coating buildup affects fit, threads are re-verified and adjusted before shipment.
Yes, we handle efficient shipping to the USA, UK, and throughout Europe. We are a leading supplier for Threaded Inserts in the Netherlands and provide high-quality Brass Threaded Inserts in Germany, as well as other international territories.
Yes. Material certificates and inspection reports are available when required. Thread fit is verified with gauges before packing.
To request a quotation for brass threaded inserts, please send your drawing along with RFQ details.
Please include:
After receiving your RFQ, the drawing is reviewed and technical clarifications are discussed when necessary. Quotation is then issued with pricing and indicative lead time before production.
