Counterbore Hole Size Chart for Pan Head Screws (UNI)
UNI counterbore hole size chart for pan head screws, including pilot hole diameters for close, normal, and loose fits, counterbore diameters, and depths (millimeters)
Pan Head Screw Counterbore Hole Chart (UNI)
| Fastener Size | Pilot Hole Diameter (mm) | Counterbore Diameter (mm) | Counterbore Depth (mm) | ||
|---|---|---|---|---|---|
| Close Fit (H12) | Normal Fit (H13) | Loose Fit (H14) | |||
| M1.6 | 1.7 | 1.8 | 2 | 3.5 | 1.5 |
| M2 | 2.2 | 2.4 | 2.6 | 5 | 2.1 |
| M2.5 | 2.7 | 2.9 | 3.1 | 6 | 2.6 |
| M3 | 3.2 | 3.4 | 3.6 | 7 | 2.9 |
| M4 | 4.3 | 4.5 | 4.8 | 9 | 3.6 |
| M5 | 5.3 | 5.5 | 5.8 | 11 | 4.5 |
| M6 | 6.4 | 6.6 | 7 | 13 | 5.4 |
| M8 | 8.4 | 9 | 10 | 18 | 6.8 |
| M10 | 10.5 | 11 | 12 | 24 | 8.3 |
About UNI Counterbore Hole Sizes for Pan Head Screws
This UNI counterbore hole size chart for pan head screws provides standardized metric dimensions according to the Italian UNI (Ente Nazionale Italiano di Unificazione) standards. It lists recommended pilot hole diameters for close fit, normal fit, and loose fit, along with the corresponding counterbore diameters and counterbore depths in millimeters.
Accurate UNI counterbore dimensions ensure proper screw seating, sufficient head clearance, and consistent mechanical performance in metric fastening applications. This reference is essential for engineers, machinists, and designers working with UNI pan head screws, including:
- Mechanical and product design projects requiring UNI pan head machine screws in metric systems.
- Machining, drilling, and fabrication processes that need precise pilot hole and counterbore preparation for standard fasteners.
- Assembly and quality control operations ensuring proper fit, alignment, and flush seating of screw heads.
Key Terms in the UNI Counterbore Hole Chart
- Pilot Hole Diameter: The drilled hole diameter defining screw shank clearance, categorized for close, normal, or loose fit.
- Counterbore Diameter: The circular recess machined to allow the UNI pan head screw to sit flush or slightly below the surface.
- Counterbore Depth: The vertical depth of the recess matching the head height of the UNI pan head screw.
- UNI Standard: The Italian UNI standard defining dimensions, tolerances, and geometry for metric-series pan head screws used in mechanical assemblies.
Referencing this UNI pan head screw counterbore hole size chart ensures consistent part design, precise manufacturing, and compliance with international metric fastener standards. Proper use of these dimensions improves assembly quality, reduces machining errors, and enhances mechanical reliability.