About this tool
Before a thread is tapped, it needs a pilot hole. As a rule of thumb for metric threads it is the nominal diameter minus the pitch, so 6 − 1 = 5 mm for M6. The chart lists for coarse and fine threads from M1.6 to M24 the common tap drill to DIN 336 and the fine, medium and coarse clearance holes to ISO 273.
For American screws to UNC and UNF it shows the usual number, letter or fraction drill and its size in millimetres. The tool also calculates pitch and minor diameters from the ISO basic profile, even for any metric size such as M7×0.75.
How it works
- Enter a thread, e.g. M6, M10x1.25, 1/4-20 or #10-32.
- Read the tap drill, clearance holes and diameters.
- Or choose coarse, fine or UNC/UNF in the chart and click a size.
Frequently asked questions
Which clearance hole should I use?
Fine for precise fits, medium as the standard for most bolted joints and coarse when several holes must line up or tolerances are large. For 3D printed parts medium is a good start because holes usually come out slightly smaller.
Does the tap drill apply to forming taps?
No. Forming taps displace the material instead of cutting it and need a larger hole, roughly nominal diameter minus half the pitch. The tool manufacturer’s data takes precedence.
Can I tap threads into 3D printed parts?
Yes, especially in PETG, ABS or nylon. The hole should be a few tenths larger than the tap drill for metal so the plastic does not crack. If printed holes come out too small, the 3D Print Dimension Calibration helps.
At what speed do I drill the pilot hole?
That depends on drill diameter and material: speed = cutting speed × 1000 / (π × diameter). The CNC Feeds & Speeds Calculator uses the same principle for end mills.