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Thread Limit Dimensions Calculator
Calculate maximum and minimum permissible dimensions for each thread element — major, pitch and minor diameter — based on tolerance class. Supports Imperial / Unified (ASME B1.1) and Metric (ISO 965-1).
Nominal Diameter
Thread SeriesAuto-fills TPI
Thread Type
Tolerance Class
Basic Formulas (ASME B1.1)
d₂ = d − 0.6495190 / n (pitch diameter)
D₁ = d − 1.0825318 / n (internal minor)
d₃ = d − 1.2269440 / n (external minor)
Td₂(2A) = 0.0015 × (d⅓ + 4√P) Allowance(1A/2A) = 0.3 × Td₂
Tolerance Classes
| Bolt (ext) | Tolerance | Allowance |
|---|---|---|
| 1A | Loose +33% | Yes (large) |
| 2A | Standard | Yes (std) |
| 3A | Tight −25% | None |
| Nut (int) | Tolerance | Allowance |
|---|---|---|
| 1B | Loose +33% | None |
| 2B | Standard | None |
| 3B | Tight −25% | None |
Thread Series
| Series | TPI vs UNC | Application |
|---|---|---|
| UNC | Base | General fasteners, rapid assembly |
| UNF | Finer | Automotive, better vibration resistance |
| UNEF | Finest | Thin-wall tubes, aerospace, fine adjustment |
Common Mating Fits
| Bolt | Nut | Application |
|---|---|---|
| 2A | 2B | Most commercial fasteners (SAE, ASTM) |
| 1A | 1B | Rapid assembly, dirty environments |
| 3A | 3B | Aerospace, high-stress precision |
Note: Calculated per ASME B1.1 formula method. For critical applications verify against ASME B1.1 tabulated values.