1. What is a mid-layer?

The intermediate sleeve is typically installed between the outer and inner tubes to fill the gap and guide movement during lifting. It ensures the inner tube moves vertically along a fixed path, minimizing wobble and instability.

Taking the 35mm round tube lift structure as an example, a common configuration pairs a 35mm outer tube with a 28mm inner tube. The middle sleeve is installed between the outer and inner tubes, allowing the 28mm inner tube to slide in smoothly for seamless lifting.

II. Main Functions of the Intermediate Sleeve

1: Guidance

When adjusting the height of an adjustable desk and chair, the inner tube must slide up and down within the outer tube. Without a suitable intermediate sleeve, the inner tube may shift, jam, or experience uneven friction. The intermediate sleeve provides stable guidance for the inner tube, ensuring smooth height adjustment.

2 Reduce shaking

A gap typically exists between the inner and outer tubes. If this gap is too large, the table or chair may wobble during use. The middle sleeve reduces the gap, ensuring a tighter fit between the tubes for enhanced structural stability.

3 Reduce friction noise

Direct metal-to-metal contact can cause friction noise and wear. Installing a plastic intermediate sleeve between the inner and outer tubes reduces direct metal friction, resulting in quieter lifting operation and minimizing tube wear.

4, Assisted Installation Location

During bulk assembly, the middle sleeve helps workers quickly align inner and outer tubes, boosting efficiency. For school furniture manufacturers, a clearly structured and easy-to-install middle sleeve reduces assembly errors.

3. Key Selection Criteria for Middle Layer Sets of 35mm Round Tubes

When selecting a middle layer sleeve for 3 5mm round tube, please verify the following parameters:

1. Is the outer tube diameter 35mm?
2. Is the inner tube diameter 28mm?
3. Does the outer tube wall thickness match?
4. Is the mid-layer material suitable for long-term use?
5. Does it come off easily after installation?
6. Is the lifting smooth?
7. Any noticeable shaking or unusual noises?

Wall thickness and tolerance may vary across manufacturers. We recommend testing a sample before placing a bulk order.

4. Why is the core material important?

The middle layer shell is typically made of plastic. For high-use products like school desks and chairs, the middle layer shell must offer flexibility, abrasion resistance, and dimensional stability. New PP material provides stable molding, good toughness, and is well-suited for mass production, making it suitable for certain desk and chair middle layer shells and plastic connectors.

In actual use, excessive brittleness can cause clips to break, while excessive softness may compromise guidance and stability. Therefore, the middle sleeve must be evaluated not only by its appearance but also by its fit after installation.

5. What should I keep in mind during installation?

When installing the middle sleeve of 35mm round tube, ensure it is oriented correctly so that the plain end and snap-fit positions align with the inner and outer tube structures. Insert the 28mm inner tube directly into the minimum inner diameter section of the middle sleeve to ensure accurate alignment. After installation, verify that the inner tube moves up and down smoothly without any noticeable binding, misalignment, or looseness.

Before mass production, we recommend conducting trial assembly tests—including up/down movement, shake, and long-term usage simulations—to confirm structural stability before proceeding with full assembly.

VI. Summary

Although compact, the mid-layer sleeve plays a critical role in guiding motion, reducing wobble and noise, and facilitating installation in height-adjustable desks and chairs. For lifting structures with 35mm outer tubes paired with 28mm inner tubes, select a mid-layer sleeve that matches the dimensions, offers stable material properties, and ensures secure installation.

For school desk and chair manufacturers, selecting the appropriate middle sleeve enhances overall stability and reduces wobbling and noise during use.