How do you calculate basic thread dimensions?
Enter the nominal major diameter and either axial pitch or threads per inch. This worksheet calculates the basic parallel 60° profile, pitch cylinder, internal minor diameter, lead and optional synchronized spindle feed. These are theoretical reference dimensions; actual manufacturing limits must come from the specified drawing and standard.
What is the difference between pitch and threads per inch?
Pitch is the axial spacing between adjacent thread crests. For a threads-per-inch entry, pitch in inches is 1/TPI; multiply by 25.4 for millimeters. Dimension units convert major diameter and axial pitch independently of the TPI count. The calculator does not infer a coarse or fine pitch from diameter alone.
Which equations define the basic sixty-degree profile?
The fundamental triangle height is H = √3P/2. Basic pitch diameter is D − 3H/4, and the internal basic minor diameter is D − 5H/4. These reductions describe the basic truncated profile. They do not supply an external rounded-root diameter, allowance, fit class or tolerance band.
60° basic triangle H = √3 × P/2; basic pitch diameter = D − 3H/4; basic internal minor diameter = D − 5H/4; lead = pitch × starts
Pitch PH
What does an M10-by-1.5 example show?
For 10 mm major diameter and 1.5 mm pitch, H = 1.299038 mm. Basic pitch diameter is 9.025721 mm, and internal basic minor diameter is 8.376202 mm. The entered pitch must match the required thread; neither value alone proves that a manufactured nut or screw meets its specification.
How do multiple starts change lead and feed?
Lead is pitch × number of starts. Two starts at 1.5 mm pitch give 3 mm axial travel per revolution. At 500 rpm, synchronized axial feed is 1,500 mm/min. Lead angle is atan(lead/(π × basic pitch diameter)); it is measured at that ideal pitch cylinder, not at the crest.
Can you use the drill comparison as a tap-drill recommendation?
No. The optional drill field reports its difference from the internal basic minor diameter. Cut taps, forming taps, material behavior and tool instructions can require different drill sizes. The calculator deliberately does not convert this comparison into a thread-engagement percentage or choose a drill for an unspecified tap.
How are measured dimensions compared with approved limits?
Enter the approved lower pitch-diameter limit, upper limit and measured value together. The result reports whether the measurement lies within those entered limits. It does not obtain tolerances for a class such as 6H or 2A, assess gauge uncertainty, or establish acceptance for tapered, 55° or trapezoidal threads.
Which input units and assumptions should you check?
Use the labeled units and measured project values. Optional fields remain blank unless their data are available; paired fields must be entered together. Basic parallel 60° geometry only, without ISO/UN tolerance classes or root-radius limits. Not NPT, BSP, Acme or forming-tap sizing; use drawing-approved limits and tool data.
| Input | Unit basis | When used |
|---|---|---|
| Nominal major diameter | in / mm | all modes |
| Axial pitch | in / mm | pitchMode:pitch |
| Threads per inch | as labeled | pitchMode:tpi |
| Number of starts (optional) | as labeled | all modes |
| Spindle speed (rpm, optional) | as labeled | all modes |
| Axial threaded length (optional) | in / mm | all modes |
| Actual drill diameter (optional) | in / mm | all modes |
| Approved pitch-diameter lower limit (optional) | in / mm | all modes |
| Approved pitch-diameter upper limit (optional) | in / mm | all modes |
| Measured pitch diameter (optional) | in / mm | all modes |
How can you compare and save different scenarios?
Calculate and save a baseline to comparison, change one input and calculate again. Review the itemized results before transferring values. Copy or share the result, download the input and result sheet, or print the worksheet. Clear changes removes the current inputs and results, and refresh starts clean.
Which related calculators help with the next step?
Use True Position Calculator and Metal Weight Calculator. Check that the measurement units and scope match before using a result as an input elsewhere.
