Diameters of Letter Drills
Complete Reference Chart: A to Z in Inches and Millimeters
This comprehensive chart provides the precise diameters of letter drills from A through Z, showing measurements in both inches and millimeters. Letter drills are essential for accurate drilling operations, particularly for sparkplug thread repairs and specialized tapping applications.
Chart Features:
- • Complete listing of letter drills from A to Z
- • Precise measurements in inches (decimal format)
- • Metric equivalents in millimeters
- • Common sparkplug thread sizes (10mm, 12mm, 14mm, 18mm)
- • Unusual and old thread specifications with TPI details
- • Essential for sparkplug thread repair operations
- • Quick reference for specialized drilling applications
Understanding Letter Drills
Letter drills are a standardized drill bit sizing system commonly used in the United States. The lettering system runs from A (smallest) to Z (largest), with each letter representing a specific diameter. This system provides precise sizing options for specialized applications, particularly in automotive and aerospace industries.
Letter drills are especially important for sparkplug thread repairs and other applications requiring precise hole sizing between standard fractional measurements. The chart also includes common sparkplug thread specifications and unusual thread sizes for reference.