Thread Calculator
Get complete metric (ISO) or unified (imperial) thread dimensions. Enter the nominal major diameter and thread pitch (mm for metric, TPI for imperial), and select the tolerance class. Results include major diameter, pitch diameter (external and internal), minor diameter (external and internal), thread depth, fundamental triangle height, tap drill size, tensile stress area, and the standard thread designation. Based on ISO 68-1 and ASME B1.1 standards for 60° thread profiles. Essential for fastener selection, thread cutting, and engineering design.
For metric: in mm (e.g., 10 for M10×1.5). For imperial: in inches (e.g., 0.5 for 1/2-13)
Metric: pitch in mm (e.g., 1.5 for M10×1.5). Imperial: TPI (e.g., 13 for 1/2-13)
H = √3/2 × P = 0.866025 × P
External thread depth (5/8 H) = 0.649519 × P
Pitch diameter: D₂ = D − 0.649519 × P
Minor diameter (ext): D₁ = D − 1.082532 × P
Minor diameter (int): D₁ = D − P
Tensile stress area:
A_t = π × ((D − 0.9382 × P) / 2)²
Where D = major diameter, P = pitch
Conversions:
1 inch = 25.4 mm
Pitch (mm) = 25.4 / TPI
Metric external thread, M10×1.5 6g
Pitch = 1.500 mm, TPI = 16.93
Major diameter: 10.000 mm
Pitch diameter: 10 − 0.6495×1.5 = 9.026 mm
Minor diameter: 10 − 1.0825×1.5 = 8.376 mm
Thread depth: 0.6495 × 1.5 = 0.974 mm
Tap drill: 10 − 1.5 = 8.5 mm
Tensile area: 58.0 mm²
Example — 1/2-13 UNC (2A):
Imperial external thread
TPI = 13, Pitch = 0.07692″ = 1.954 mm
Pitch diameter: 0.5 − 0.6495/13 = 0.4500″
Minor diameter: 0.5 − 1.0825/13 = 0.4167″
Tap drill: ~0.423″ (27/64″)
What are the critical thread dimensions?
For any screw thread, the key dimensions are: Major diameter — the largest diameter of the thread (crest for external, root for internal). Minor diameter — the smallest diameter (root for external, crest for internal). Pitch diameter — the theoretical diameter where thread width equals gap width. For a standard M10×1.5 bolt: Major = 10.000 mm, Pitch diameter ≈ 9.026 mm, Minor ≈ 8.376 mm. Thread depth = 0.6495 × pitch = 0.974 mm. These dimensions determine thread fit, strength, and interchangeability.
What is the difference between 6g and 6H thread tolerance?
6g is the standard tolerance class for external threads (bolts/screws), while 6H is the standard for internal threads (nuts). The lowercase "g" indicates an external thread with a basic size below nominal (allowance), and uppercase "H" indicates an internal thread with basic size at nominal (no allowance). A 6g/6H fit is the standard medium-quality fit for general engineering. 4g6g/4H5H provides tighter tolerances for precision work. 8g/7H allows looser fits for quick assembly or where threads may be damaged (e.g., automotive spark plugs).
How do I calculate thread depth?
For standard 60° ISO metric threads: Thread depth = 0.6495 × Pitch. For example, M10×1.5: depth = 0.6495 × 1.5 = 0.974 mm. For UN threads (also 60°): Depth (inches) = 0.6495 / TPI. For a 1/2-13 bolt: depth = 0.6495/13 = 0.0500 inches. The total thread height from root to crest = 5/8 × H = 5/8 × 0.8660 × Pitch = 0.5413 × Pitch for external threads. Internal threads have a slightly different profile with the root rounded or flat. These calculations are per ISO 68-1 and ASME B1.1 standards.
What does the thread designation M10×1.5 6g mean?
M = Metric (ISO) thread profile (60° angle). 10 = nominal major diameter in millimeters. ×1.5 = thread pitch in millimeters (1.5 mm between crests). 6g = tolerance class for external threads. For imperial: 1/2-13 UNC-2A means: 1/2" nominal diameter, 13 threads per inch, UNC = Unified Coarse, 2A = tolerance class 2 (medium) for external (A) threads. Metric fine threads are designated MF (e.g., M10×1.25). Understanding these designations ensures proper mating of threaded components and correct tool selection for thread cutting.
🔗 Related Calculators
📐 Formula
H = √3/2 × P = 0.866025 × P
External thread depth (5/8 H) = 0.649519 × P
Pitch diameter: D₂ = D − 0.649519 × P
Minor diameter (ext): D₁ = D − 1.082532 × P
Minor diameter (int): D₁ = D − P
Tensile stress area:
A_t = π × ((D − 0.9382 × P) / 2)²
Where D = major diameter, P = pitch
Conversions:
1 inch = 25.4 mm
Pitch (mm) = 25.4 / TPI
📝 Example Calculation
Metric external thread, M10×1.5 6g
Pitch = 1.500 mm, TPI = 16.93
Major diameter: 10.000 mm
Pitch diameter: 10 − 0.6495×1.5 = 9.026 mm
Minor diameter: 10 − 1.0825×1.5 = 8.376 mm
Thread depth: 0.6495 × 1.5 = 0.974 mm
Tap drill: 10 − 1.5 = 8.5 mm
Tensile area: 58.0 mm²
Example — 1/2-13 UNC (2A):
Imperial external thread
TPI = 13, Pitch = 0.07692″ = 1.954 mm
Pitch diameter: 0.5 − 0.6495/13 = 0.4500″
Minor diameter: 0.5 − 1.0825/13 = 0.4167″
Tap drill: ~0.423″ (27/64″)