Self-Tapping Threaded Insert Pilot Hole Size Charts for Metal, Plastic & Wood.

Choosing the correct pilot-hole size is critical when utilising self-tapping products. It ensures each threaded insert sits flush to your working surface, grips properly and delivers maximum pull-out strength, all without damaging the parent material.

This guide provides complete pilot-hole size data for the most commonly utilised threaded inserts for wood, plastics and metals.

Quick Navigation:

• Self-Tapping Threaded Screw Inserts - for wood, plastics and non-ferrous metals.

• Self-Tapping Threaded Inserts for Wood - Suitable for hard/soft wood and available with or without a flange.

• FAQs

How to Use These Charts.

How to select the correct pilot size from these tables.

Self-tapping threaded screw inserts show a pilot hole size range (e.g. 8.9–9.4 mm).

This range gives flexibility to fine-tune the fit depending on the material.

• Use the lower end of the range for softer materials (plastics, softwoods). This gives a tighter fit, improving pullout resistance.

• Use the upper end for harder materials (aluminium, dense hardwoods, harder plastics). This produces a slightly looser fit, which is easier to drive and reduces the risk of thread galling or cracking.
  
  

Threaded Inserts for Wood have a fixed value for the pilot hole.
This is due to them not cutting their own threads in the same way as self-tapping screw inserts for metal or plastic, utilising specialised burrs rather than a traditional thread.

This fixed pilot size is chosen to achieve two things:

• Maximum grip in both softwood and hardwood.

• Controlled drive torque, so the insert can be installed securely without splitting the timber.

Self-Tapping Threaded Screw Insert Pilot Hole Chart.

SHOP THREADED SCREW INSERTS.

Note: M3.5 uses a fixed pilot of 5.3 mm with a −0/+0.1 mm tolerance (no range). 

Quick Installation Notes:

• Metals: Use the upper end of the pilot range for aluminium and other light alloys to reduce drive torque and thread galling issues.

• Plastics: For softer plastics, choose the lower value; for filled or harder plastics, choose the higher value.
  If you need a plastic-specific insert solution, consider our guide on Heat-Set Brass Inserts and check out our pilot-hole guide on these, too.

• Wood: These stainless steel or brass self-tapping inserts can also be used in wood.
  Use the lower pilot-hole range for softwoods, the upper range for hardwoods.
  
  

Self-Tapping Threaded Inserts for Wood Pilot Hole Chart.

The tables below include non-flanged and flanged variants.
Flanged inserts sit flush and prevent over-driving, while non-flanged inserts allow concealed installation.

SHOP THREADED INSERTS FOR WOOD.

Standard Wood Inserts.

Flanged Wood Inserts.

Quick Installation Notes:

• Driving torque: If the insert binds early in dense hardwood, try a +0.2 mm increase on the pilot size (S). For ultra-dense hardwoods, consider self-tapping threaded inserts instead of a wood-specific option.

• Socket tools: Always use the specified socket size to avoid damaging the internal hex or the surrounding material.

FAQs

Q: What pilot-hole size should I use for self-tapping threaded inserts in metal, plastic, or wood?

A: Use the size or range specified for the insert’s external thread. Choose the lower value for softer materials and the upper value for harder materials to ensure proper grip and clean thread cutting.

Q: How do I choose the correct pilot-hole range for self-tapping threaded screw inserts such as M6, M8, or M10?

A: Match the insert’s outer diameter to the chart and use the listed pilot-hole range. Softer materials use the lower end; harder materials use the higher end for easier driving and secure installation.

Q: Why do self-tapping threaded inserts require different pilot-hole sizes depending on the parent material?

A: Softer materials compress and need a tighter pilot for strength. Harder materials resist cutting, so a slightly larger pilot reduces torque and prevents cracking or galling.

Q: What happens if the pilot-hole size is too small or too large?

A: If the pilot hole is too small, the insert can bind, require excessive torque, or cause cracking, while a hole that is too large reduces grip and pull-out strength; using the correct pilot size ensures proper seating and reliable performance.