ᐅ Billy Regal screws are too short – which alternative sizes are suitable?

Hello everyone,

I’m currently facing an issue with my Billy bookshelf. The screws provided for wall mounting are clearly too short, so they don’t anchor deeply enough into the wall. I want to switch to replacement screws but am unsure about the correct size that would be suitable and secure without damaging the shelf or compromising stability.

The shelf has the standard drill holes from Ikea, and the screws are currently 25 mm (1 inch) long and M4. I assume longer screws (maybe 40 to 50 mm (1.5 to 2 inches)) would be more appropriate, especially if I use wall plugs with a length of 50 mm (2 inches). But I don’t want to buy randomly—are there recommendations or experience on the ideal screw length and possibly diameter to securely mount the shelf on common drywall (plasterboard) or concrete walls?

Note: I cannot set the wall plugs deeper than 50 mm (2 inches); the hole cannot be extended due to existing installations.

I’d appreciate well-informed advice, preferably from professionals or experienced DIYers who have dealt with this before.

Best regards!

flogla schrieb:
The shelf has the standard drill holes from Ikea, the screws are currently 25 mm long and M4.

The 25 mm (1 inch) long M4 screws are usually sufficient for standard assembly directly into furniture or softwood. However, caution is needed when mounting on walls, especially on drywall panels. To securely fix a Billy shelf, I recommend screws with a length of at least 50 mm (2 inches) combined with appropriate wall plugs (e.g., cavity anchors or molly bolts) designed for the specific wall type.

The screw diameter should ideally not be too large, as the pre-drilled holes in the shelf are intended for M4 screws. M5 screws are often too thick and can damage the shelf material.

Summary:
- Screws: M4, 50 mm (2 inches) length
- Wall plugs: suitable for the wall (cavity anchors for drywall, expansion plugs for concrete)
- Important: The wall plug should be embedded at least 50 mm (2 inches) deep in the wall to ensure load capacity.

Never use screws shorter than the wall plugs.

Hello,

I’m adding a short guide that I often use when working with Billy shelves:

1. Screw size: The original is M4, and it’s best to keep this, as the shelf has pre-drilled holes for M4 screws. Larger screws could damage the hole or even split the shelf component.

2. Screw length: As Dopoki already mentioned, 50 mm (2 inches) is ideal if the wall anchor is also 50 mm (2 inches) long. You need at least 10-15 mm (0.4-0.6 inches) of screw penetration into the shelf wood to ensure good hold on both sides.

3. Choice of anchor: For drywall (plasterboard), it’s best to use special hollow wall anchors. Regular expansion anchors often don’t grip properly in drywall.

4. Assembly tip: Pre-drilling is recommended when using longer screws to prevent the wood from splitting.

Common mistakes:
- Screws too short, resulting in poor holding strength
- Wrong type of anchor (e.g., expansion anchors used in drywall)
- Screws too thick, not fitting into the shelf

Conclusion: If you use a 50 mm (2 inches) hollow wall anchor with a matching 50 mm (2 inches) M4 screw, you should be on the safe side. Before purchasing, check the shelf holes again, but 4 mm (0.16 inches) screws usually fit.

M4 screws with a length of around 50 mm (2 inches) work well. It is important that the screws penetrate the shelf and embed at least 10 mm (0.4 inches) into the wood. For drywall, use hollow wall anchors; for concrete, use standard anchors and screws.

SauDietmar schrieb:
Pre-drilling is useful when using longer screws to prevent the wood from splitting.

That makes sense, thanks. I only have thin particleboard as the back panel for the shelf, so I assume that could be particularly critical when screwing in longer screws?

Dopoki schrieb:
The screw diameter should ideally not be too large, as the pre-drilled holes in the shelf are sized for M4 screws.

I measured, and the holes are indeed pre-drilled to 4 mm.

If I buy 50 mm M4 screws but don’t get enough thread grip in the wall (for example, with very soft material or if I use anchors that are too short), could I still secure the shelf additionally with brackets underneath? Or does anyone have suggestions on how to best distribute the load? I want the shelf to remain stable, especially when loaded later on (books, up to 30 kg per shelf).