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Trusted by 100,000+ Customers

Heat-Lok

PSM Heat-Lok is a special insert designed primarily for thermoplastic applications where you want low stress insertion, strong torque and pull-out performance, and high alignment reliability. It is a double-ended, self-aligning brass insert that is installed using heat (rather than ultrasonics), making it ideal for amorphous plastics and precision applications.

Advantages

Heat-Lok Selection of Inserts

Key Features & Strengths

Low stress generation: Heat-Lok is designed to minimize radial or bursting stresses inside the plastic boss, which is especially important for amorphous thermoplastics.
Double-ended design: This assists automatic feeding in high-speed production and allows insertion from either side.
High torque resistance: The insert maintains strong thread engagement against twisting or loosening under load.
Self-aligning during installation: Its geometry helps center it in the hole as it heats and inserts.
Available in both insert and stud forms, and with headed variants, giving flexibility in mounting and design.

ISO Metric

Unified

Specifying an Insert & Stud

Boss Design Specification

Hole Preparation

Molded holes are recommended wherever possible. The taper on a molded hole should be 0.5° inclusive and the hole diameter recommended should apply at the point reached by the bottom of the insert. The top of the hole should not be chamfered or counterbored and care must be taken to avoid bell mouthing. Hole diameter tolerance:-0.00 +0.10mm.

Molding Practice

Mold design should be arranged to eliminate residual stresses in the area of the boss or hole into which the insert is to be installed.

Installation

Heat-lok has been designed for installation using heat rather than ultrasonics, since direct heat best suits the plastic flow required by the insert profile.

Wall Thickness

A general guide to minimum wall thickness is given in the data table but this will vary depending upon the nature of the plastic. Where thinner walls are required these can often be accommodated, but consultation with the PSM Technology Centre or local sales office and pre-production testing is strongly advised.

Performance Data

The complexity of materials and variations in service conditions make it impossible to detail fastener performance for specific applications. The chart below gives a general guide and show the relative performance of the inserts in the range.

Enhance Your Assembly with Our Precision Heat-Lok Inserts

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Frequently Asked Questions About Heat-Lok Inserts

What is a Heat-Lok Insert?

A Heat-Lok Insert (HL/HLH/HLTS/HLHS) is a brass threaded insert engineered specifically for heat staking into amorphous thermoplastics that are sensitive to knurling. Its design avoids relying on an aggressive knurl pattern for retention, instead using a gripping geometry suited to plastics that could crack or stress-fracture under a standard knurled insert.

What does "knurling sensitive" mean for a plastic material, and why does it matter for insert selection?

Some amorphous thermoplastics — such as polycarbonate and certain ABS blends — can be prone to stress cracking when a standard, aggressively knurled insert is installed, because the sharp knurl pattern concentrates stress at many small points around the insert. A Heat-Lok Insert is designed to provide secure retention in these materials without relying on an aggressive knurl pattern that could initiate cracking.

What is the difference between HL, HLH, HLTS, and HLHS Heat-Lok variants?

HL, HLH, HLTS, and HLHS are variants within PSM’s Heat-Lok range, differing in head/flange style, length, and thread specification to suit different boss designs and installation requirements. All variants share the same brass construction and core design principle optimised for heat-staking into knurl-sensitive amorphous thermoplastics. PSM’s dimensional data sheet specifies the exact distinguishing features of each code.

What amorphous thermoplastics are compatible with Heat-Lok Inserts?

Heat-Lok Inserts are designed for amorphous thermoplastics that are sensitive to knurling, commonly including polycarbonate (PC), ABS, and certain ABS/PC blends. These materials are widely used in applications such as electronics housings and automotive interior trim, where Heat-Lok Inserts provide reliable thread retention without the stress-cracking risk of an aggressively knurled insert design.

How does a Heat-Lok Insert compare to a standard knurled insert in the same plastic material?

A standard knurled insert relies on an aggressive external knurl pattern biting into the plastic for retention, which works well in ductile thermoplastics but can stress-crack more brittle amorphous plastics. A Heat-Lok Insert is specifically engineered to provide reliable retention in these knurl-sensitive materials without the same cracking risk, making it the safer choice for amorphous, crack-prone plastic types.