Self-Tapping Screw Pilot Hole Size Chart for Metal and Plastic
This guide from Simfix helps choose the right pilot hole for 3.5, 4.2 and 4.8 mm self-tapping screws in mild steel, aluminium and plastic. Includes practical charts and common fixes.
- Covers 3.5, 4.2, and 4.8 mm self-tapping screw sizes.
- Covers mild steel, aluminium, and plastic materials.
- Includes practical pilot hole charts and fixes.
What This Page Covers
- Pilot hole diameters for 3.5, 4.2, and 4.8 mm self-tapping screws.
- Recommendations for mild steel (1–3 mm thickness).
- Adjustments for aluminium (0.1 mm larger than steel).
- Special considerations for plastic (grade, wall thickness, boss design).
- Practical starting points and common fixes.
Article Content
For a self-tapping screw, the pilot hole must be smaller than the screw's outside diameter but large enough to prevent excessive driving torque. In 1 to 3 mm mild steel, a 4.2 mm screw normally starts with a 3.2 to 3.3 mm pilot hole. A 4.8 mm screw normally starts with 3.7 to 3.8 mm. Aluminium usually needs a hole about 0.1 mm larger. Plastic needs a different approach because grade, wall thickness and boss design change the answer. The charts below are practical starting points for non-critical applications.
- In 1–3 mm mild steel, a 4.2 mm self-tapping screw uses a 3.2–3.3 mm pilot hole.
- In 1–3 mm mild steel, a 4.8 mm self-tapping screw uses a 3.7–3.8 mm pilot hole.
- Aluminium pilot holes are typically 0.1 mm larger than the steel recommendation.
- Plastic pilot hole size depends on material grade, wall thickness, and boss design.
- The provided charts serve as practical starting points for non-critical applications.
Facts Index
| Entity | Attribute | Value | Confidence |
|---|---|---|---|
| Self-Tapping Screw Pilot Hole Size Chart for Metal and Plastic | author | Simfix Team | high |
| Self-Tapping Screw Pilot Hole Size Chart for Metal and Plastic | publish_date | 2026-08-04T20:01:13Z | high |
Who Is This For
- DIY enthusiasts and professionals who need to drill pilot holes for self-tapping screws in metal and plastic.
- Manufacturing and repair technicians working with sheet metal or aluminium.
- Engineers designing plastic parts with self-tapping screw bosses.
Frequently Asked Questions
Who wrote this guide?The Self-Tapping Screw Pilot Hole Size Chart for Metal and Plastic was authored by the Simfix Team.
When was this guide published?The Self-Tapping Screw Pilot Hole Size Chart for Metal and Plastic was published on 2026-08-04.
What pilot hole size is recommended for a 4.2 mm self-tapping screw in mild steel?For a 4.2 mm self-tapping screw in 1–3 mm mild steel, the recommended pilot hole is 3.2 to 3.3 mm.
What materials are covered by the pilot hole chart?The chart covers mild steel, aluminium, and plastic materials for 3.5, 4.2, and 4.8 mm self-tapping screws.
How does the pilot hole size differ for aluminium compared to steel?For aluminium, the pilot hole should be about 0.1 mm larger than the size recommended for mild steel.