Tap drill diameter

How to use the calculator

Select the standard (Metric / UNC / UNF) and thread size - the calculator will show the diameter of the drill bit for the thread, the percentage of profile filling, as well as the CNC cycle. For non-standard threads, use manual entry: "M10x1.25" or "3/8-16".

The “Material” and “Priority” parameters affect the calculation for the forming tap: aluminum allows for more filling, stainless steel and HRSA require a decrease in filling.

What is the difference between a tap and a rolling machine?

Cutting tap—cuts material and forms chips. Drill diameter = D − Pitch. Universal for all materials and types of holes.

Roller—presses the material without chips. The drill diameter is larger, the filling is smaller (55–70%). The thread strength is higher - the metal is compacted and not cut. Requires lubricating coolant and precise hole Ø ±0.02 mm.

Metric, UNC, UNF - what is the difference for selecting Ø

All three standards use the same calculation formula, but set the step differently. Metric - pitch in mm (M6×1.0 → pitch 1.0 mm). UNC and UNF set TPI (threads per inch): for 1/4-20 pitch = 25.4/20 = 1.27 mm. The calculator recalculates TPI automatically.

Frequently Asked Questions

Why is one diameter written on the tap, but I found another? Tables from different manufacturers give diameters for a specific thread tolerance range (6H, 7H) and material. The D−P formula is a basic guideline. For the exact tolerance range, check the tap catalog.

For the rolling tool, you need to know exactly Ø - why? The rolling tool does not allow deviation: if the hole is small, the moment will critically increase and the rolling tool will break; if it is large, the thread profile will be incomplete. Tolerance on the Ø of the hole for the rolling pin: ±0.01–0.02 mm from the calculated one.

What percentage of thread fill is sufficient for a bolted connection? For most connections, 60–75% provides more than 90% of the design thread strength. An increase from 75% to 100% gives an increase in strength of less than 5%, but the cutting torque increases by 2–3 times.

Taps, rolling tools and measuring tools for thread control are in our catalog. We select according to material and tolerance range.