STEP 2: How to choose the length of profiles, screws and threaded rods

How do you choose the right screw or rod length in Michno System? This guide explains how to measure wall deviations, read laser measurements and choose between L50, L80, L130 and L180 for a stable, level structure.

Choosing the correct length of profiles (screws/threaded rods) is one of the key stages of Michno System installation. It determines whether the structure will have the right adjustment range, whether plugs and discs will work within their optimal range, and whether the entire drywall lining will remain rigid and even.

In practice, selecting the screw length is simple — provided that the wall plane has first been correctly set out and the maximum deviation of the substrate has been measured.

Below we show, step by step, how a contractor should choose the right screw lengths based on cross-line laser measurements, using examples from a real construction site.

Why does the correct screw length matter?

In Michno System, the screw acts as an adjustable spacer that moves the profile away from the uneven wall and allows it to be set perfectly in plane.

If the screw is too short:

• there will not be enough range to move the structure away from the wall,

• the disc will not work in the required adjustment range,

• the profile may “pull” the plasterboard, creating a local depression in relation to the whole plane.

If it is too long:

• the profile will locally “push out” the plasterboard, causing a bulge in relation to the whole wall, ceiling or plane.

That is why the screw length must always be matched to the actual curvature of the wall.

Step 1: Set the laser plane and mark the reference line

After setting the laser and finding the ideal plane (as described in the previous article), it must be “transferred” onto the wall. In practice, contractors do it as follows: They mark the points where the laser line passes over the wall with a marker. These points can be marked on: both ends of the wall, the ceiling, the floor — if there is enough space. This makes it easy to recreate the line later, even after changing the laser position. This preparation makes it easier to measure the actual wall deviations at the next stage.

Step 2: Measure the distance from the laser plane to the wall

Now that the laser shows the ideal plane, we can measure how far the substrate deviates from it. Measure in several points: bottom of the wall middle top both corners any place that looks suspicious, such as humps or dips Example from the renovation shown in the video below: at the highest point, the deviation is 3 cm, in other places it reaches up to 5 cm, on the opposite wall, deviations reach up to 10 cm. This measurement is crucial — it is the basis for choosing the profile length.

Step 3: Choose the profile length

Michno System profiles come in different lengths. Each length provides a different adjustment range.

L50 screw (50 mm)

Working range: from 1 cm to about 3 cm away from the wall.

This solution is intended for straight walls and ceilings.

L80 screw (80 mm)

Working range: from 1 cm to about 5 cm away from the wall.

Ideal when the deviation is no more than 3–5 cm.

L130 screw (130 mm)

Working range: from 6 cm to about 10 cm away from the wall.

Use it when the wall deviation exceeds the working range of L80.

L180 screw (180 mm)

Working range: from 11 cm to about 15 cm away from the wall.

This option is dedicated especially to suspended ceilings where lighting, air conditioning or other installations need to be hidden under the board.

Step 4: Check profile adjustment

After choosing the profile length, it is worth checking whether:

✔ it can work within the required adjustment range

✔ it is anchored in the wall to a minimum depth of 32 mm

✔ all profiles are in one line; discs closer to the wall will “pull” the plasterboard, while those farther away will “push it out”

Once these conditions are met, the structure will be durable and resistant to vibrations, deflection and board stresses.

The most common mistakes when choosing screw length

❌ Choosing profiles “by eye”, without measuring deviations.

❌ Using a profile that is too short — no possibility of moving the structure away.

❌ Using a profile that is too long — the disc works too far from the adopted plane line.

❌ Measuring only at one point instead of along the full height.

Each of these mistakes can lead to unevenness or instability of the structure.

Choosing profiles is simple when it is based on real measurements, not guesswork. This allows the Michno System structure to work stably, precisely and predictably — regardless of wall curvature.