3M™ Dual Lock™ SJ3870 Reclosable Fastener

3M™ Dual Lock™ Reclosable Fastener SJ3870, High-performance removable fastening

The 3M™ Dual Lock™ Reclosable Fastener SJ3870 offers a high-performance removable fastening solution without screws or permanent glue. It snaps together and pulls apart in a click, hundreds of times.

Its interlocking mushroom-shaped stems generate exceptional holding strength, far superior to standard Velcro. Ideal for demanding industrial applications.

Features a high-tack acrylic adhesive backing for rapid application on smooth surfaces. Compatible with the 3M™ Dual Lock™ range for versatile and reliable assemblies.

What is the 3M™ Dual Lock™ Reclosable Fastener SJ3870?

The 3M™ Dual Lock™ Reclosable Fastener SJ3870 is a removable fastening system based on molded polypropylene mushrooms. Two strips interlock with each other to create a strong bond, without screws or permanent glue.

Unlike standard Velcro (hooks + loops), Dual Lock™ uses two identical sides: each strip features rigid stems that snap into one another. The result: significantly higher holding power and a clean, repeatable assembly/disassembly process.

The SJ3870 is the high-performance reference of the range. It incorporates a pressure-sensitive acrylic adhesive on the back, facilitating application on flat, smooth, or slightly textured surfaces.

How the Dual Lock™ system works

The polypropylene stems deform slightly upon engagement and then snap back into shape. This mechanism generates an audible click when closing, an immediate confirmation of a secure attachment.

Opening is achieved by peeling (peel force, not shear force). Consequently, the fastener is highly resistant to vibrations and lateral stress, where a simple adhesive would fail.

Product	Technology	Stem density	Shear strength	Typical usage
3M™ Dual Lock™ SJ3870	PP stems-2 identical sides	400 stems/sq in	Very high	Industrial fastening, panels, electronic housings
3M™ Dual Lock™ SJ3550	PP stems-2 identical sides	250 stems/sq in	High	POS displays, light assembly
Industrial Velcro® (hook/loop)	Textile hooks + loops	-	Moderate	Textile, light fastening

Technical specifications of the SJ3870: density, dimensions, and adhesive

The 3M™ Dual Lock™ SJ3870 is a reclosable fastener with a medium density of 170 stems/cm². It is the standard reference in the Dual Lock range, balancing engagement force with ease of detachment.

The backing is made of black polypropylene, reinforced with an acrylic foam back. This construction provides good resistance to impact and vibrations.

The high-performance acrylic adhesive allows for direct bonding to most smooth or slightly textured surfaces: metal, ABS plastic, polycarbonate, glass. No screwing, no riveting.

The SJ3870 is designed to be used face-to-face with itself or with other compatible Dual Lock references (SJ3550, SJ3560). Two identical strips interlock and release on demand.

Reference	Density (stems/cm²)	Adhesive type	Typical usage
SJ3870	170	High-performance acrylic	Standard removable fastening, indoor/outdoor use
SJ3550	250	High-performance acrylic	High-strength fastening, heavy loads
SJ3560	400	High-performance acrylic	Very high-strength fastening, intense vibrations
Classic Velcro®	N/A (hook/loop)	Variable	Textile, light use, limited cycles

Unlike traditional Velcro®, the Dual Lock SJ3870 withstands thousands of opening/closing cycles without significant loss of performance. Ideal for applications requiring regular disassembly.

Comparison: SJ3870 vs. other Dual Lock™ references and removable fastening systems

SJ3870 (250 stems/dm²) vs. SJ3871 (400 stems/dm²)

The SJ3870 features a density of 250 stems per dm², compared to 400 for the SJ3871. Fewer stems mean a slightly more flexible engagement and an opening/closing cycle that is easier to maneuver.

The SJ3871 develops a higher peel force: it is preferable for heavier loads or intense vibrations. The SJ3870 remains the standard choice for the majority of common industrial applications.

Both references are self-mating: one SJ3870 strip assembles with another SJ3870, with no need for opposing loops or hooks. This is the fundamental advantage of the Dual Lock™ system compared to classic Velcro.

Velcro alternatives and other removable fastening systems

Traditional Velcro (hook/loop) such as 3M™ SJ3526 offers a softer gripping surface that is quieter to open. It is better suited for textiles and light-duty applications.

Dual Lock™ SJ3870, meanwhile, generates an audible engaging click and offers better resistance to shear loads. This is a key point in environments subject to mechanical stress.

Product	Stem density	Type	Shear strength	Typical usage
3M™ Dual Lock™ SJ3870	250 stems/dm²	Self-mating	High	Standard industrial fastening
3M™ Dual Lock™ SJ3871	400 stems/dm²	Self-mating	Very high	Heavy loads, vibrations
3M™ Velcro SJ3526	N/A (hook/loop)	Hook + loop	Moderate	Textile, light applications
Velcro® Industries, standard	N/A (hook/loop)	Hook + loop	Low to moderate	General use, office, textile

Applications and fields of use for Dual Lock™ SJ3870

The Dual Lock™ SJ3870 is designed for any situation where a fastening must be both strong and removable without leaving a trace or damaging surfaces.

Its high-performance acrylic adhesive backing allows it to bond to a wide variety of materials: plastic, painted metal, glass, composites. Ideal for both industrial and interior design settings.

Here are the most common fields of application:

• Automotive industry: attachment of trim panels, wiring, electronic housings
• Electronics and display: mounting signage, screens, control boxes
• Commercial design: installation of displays, lightweight partitions, decorative elements
• Transport and mobility: fastening components in commercial vehicles, trains, buses
• Medical industry: securing equipment to sensitive surfaces

The SJ3870 stands out for its ability to support high shear loads while allowing for clean and repeated detachment. This is a decisive advantage over permanent screw or glue solutions.

Product	Type	Shear strength	Open/close cycles	Typical usage
3M™ Dual Lock™ SJ3870	Rigid stems (type 400)	Very high	≥ 1,000	Industrial, automotive, display
3M™ Dual Lock™ SJ3550	Flexible stems (type 250)	High	≥ 1,000	Light assembly, consumer electronics
Standard industrial Velcro®	Textile hook / loop	Moderate	≥ 10,000	Textile, lightweight interior design
Velcro® ALFA	Reinforced hook / loop	High	≥ 5,000	Light structural fastening, furniture

For applications requiring vibration or temperature resistance, the SJ3870 remains the most robust choice in its category.

Application tips and best practices for optimal fastening

Surface preparation is the most critical step. Clean thoroughly with isopropanol or a suitable degreaser before any application.

The surface must be dry, clean, and free of dust. Any residual contamination significantly reduces the tape's adhesion.

Apply the SJ3870 by exerting firm and uniform pressure along the entire length of the tape. Using a roller is recommended to ensure optimal contact with the substrate.

Allow for a 24-hour maturation time after application before stressing the fastener. The acrylic adhesive reaches its full performance after this period.

For applications on curved or irregular surfaces, cut the tape into short segments. This facilitates the tape's adaptation to the part profile and prevents edge lifting.

Key best practices to remember:

• Ideal application temperature: between +15 °C and +38 °C
• Avoid untreated low-surface-energy surfaces (raw PE, PP)
• On painted or lacquered metal, check the primer's durability before application
• Do not stretch the tape during application to avoid internal stress
• Store unopened rolls away from heat and humidity

The Dual Lock SJ3870 stands out with its mechanical stem-based attachment system: the two strips interlock, requiring no precise alignment. A simple press is sufficient to close the fastener.

For a clean detachment, apply tension with a gradual peel rather than a sudden pull. The fastener remains reusable for hundreds of cycles.

FAQ - 3M™ Dual Lock™ Reclosable Fastener SJ3870

1. What is the difference between Dual Lock™ SJ3870 and classic Velcro?

The 3M™ Dual Lock™ SJ3870 does not use hooks and loops like Velcro. It works with mushroom stems that interlock with one another on both sides.

Result: a more rigid, vibration-resistant attachment that produces an audible click upon closing. Ideal for demanding industrial applications.

2. Is the SJ3870 resistant to chemicals and UV light?

Yes. The SJ3870 is formulated from polypropylene, a material that is naturally resistant to many common chemicals and UV light.

It is suitable for outdoor environments or areas exposed to prolonged sunlight without premature degradation of the stems or the adhesive.

3. How many open/close cycles can it support?

The Dual Lock™ SJ3870 supports approximately 1,000 engagement/disengagement cycles without significant performance loss. This is far beyond standard Velcro.

This durability makes it a relevant choice for removable panels, regular maintenance equipment, or interchangeable displays.

4. Which surfaces can the SJ3870 be bonded to?

The SJ3870's adhesive backing is compatible with smooth and clean surfaces: metal, rigid plastic, glass, lacquered or painted wood.

For porous or textured surfaces, a 3M adhesion promoter (such as Primer 94) significantly improves long-term adhesion.

5. Can the SJ3870 be cut to the desired length?

Yes, the tape is easily cut with scissors or a utility knife. No special tools are required.

At Dagobert Industrie, we recommend cutting lengths adapted to each application to optimize contact surface and ensure reliable fastening.

6. Can the SJ3870 be combined with other Dual Lock™ references?

Yes. The SJ3870 is compatible with other 3M Dual Lock™ references with the same or similar stem density (170 or 250 stems/cm² types).

However, it is not designed to be paired with conventional Velcro: the two systems operate on different mechanical principles.