Tap & Drill Bit Size Chart
Free tap drill size chart. Find 75% thread tap drills for metric ISO, UNC and UNF threads in mm and decimal inches, with close-fit and free-fit clearance holes. Search and filter, fully offline.
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What is Tap & Drill Bit Size Chart?
The Tap & Drill Bit Size Chart lists the correct pilot drill for every common thread: metric ISO coarse and fine from M1 to M20, plus the UNC and UNF inch series. Each row shows the 75% thread tap drill in millimetres and decimal inches, and inch threads include close-fit and free-fit clearance holes for the screw. Values are computed from the standard formulas, so the chart stays consistent across the whole list, offline.
Key Benefits
- Right drill size at a glance before you risk a broken tap
- Metric and inch threads side by side with decimal equivalents
- Close-fit and free-fit clearance holes for locating versus sliding screws
- 75% thread formula balances strength against tapping torque
- Offline workshop reference with search and system filters
Common Use Cases
- •Drilling and tapping threads in steel, aluminium or 3D-printed parts
- •Choosing between UNC and UNF for a repair
- •Cross-referencing metric drills with inch bits in the shop
- •Planning clearance holes for brackets and plates
- •Teaching machining students the 75% thread rule
How to Find a Tap Drill Size
- Find your thread: Search by the thread callout, like M6x1.0 or 1/4-20, or filter to metric, UNC or UNF and browse the list.
- Read the tap drill: The tap drill column shows the 75% thread size in millimetres and decimal inches, calculated from the major diameter and pitch or threads per inch.
- Choose the clearance fit: For through holes the screw passes, check the close-fit or free-fit clearance column instead of the tap drill.
Key Features
- Metric ISO coarse and fine threads from M1 to M20
- UNC and UNF inch series from #0 to 3/4 inch
- 75% thread tap drills in both millimetres and decimal inches
- Close-fit and free-fit clearance hole sizes for inch threads
- Search by thread label, major diameter or drill size