Plan de l'article
This guide details standards for nominal lengths and thread lengths of bolts, screws, and studs, based on ISO 888:2012 and related tolerances from ISO 4759-1. The structure is as follows:
- Introduction to Length Standards
- Nominal Length Standards
- Thread Length Standards
- Key Notes and Calculations
- Foire aux questions (FAQ)
Introduction to Length Standards
Standards for nominal lengths and thread lengths of bolts, screws, and studs ensure interchangeability, design consistency, efficient material management, improved production efficiency, and compliance with industry regulations. These standards, aligned with ISO 888:2012 for lengths and ISO 4759-1 for tolerances, facilitate uniform manufacturing and application across sectors like automotive, construction, and machinery.
Adopting standardized lengths minimizes installation issues, simplifies inventory, and reduces costs. Product grades A, B, and C define tolerance levels, with A offering the tightest for precision applications, B for general use, and C for less critical scenarios.
- Interchangeability: Enables seamless replacement from different manufacturers.
- Design Consistency: Promotes uniform engineering practices.
- Material Management: Streamlines stock control and procurement.
- Production Efficiency: Optimizes manufacturing processes.
- Regulatory Compliance: Meets national and international norms.
These guidelines provide practical direction for selecting appropriate lengths, ensuring structural integrity and performance in fastened assemblies.
Nominal Length Standards
Nominal lengths for bolts, screws, and studs follow ISO 888:2012, with tolerances per ISO 4759-1. The table below lists preferred nominal lengths (l) in mm, along with minimum and maximum values for grades A, B, and C. Avoid lengths in parentheses where possible, as they are secondary preferences.
Grade A tolerances are tighter (js15 for l ≤ 150 mm, js17 for l > 150 mm), suitable for high-precision needs. Grade B uses js17 uniformly, balancing cost and accuracy. Grade C applies js17 for l ≤ 150 mm and ±IT17 for larger sizes, for economical applications.
| Nominal Length l (mm) | Grade A (mm) | Grade B (mm) | Grade C (mm) | |||
|---|---|---|---|---|---|---|
| Min | Max | Min | Max | Min | Max | |
| 2 | 1.80 | 2.20 | – | – | – | – |
| (2.5) | 2.30 | 2.70 | – | – | – | – |
| 3 | 2.80 | 3.20 | – | – | – | – |
| 4 | 3.76 | 4.24 | – | – | – | – |
| 5 | 4.76 | 5.24 | – | – | – | – |
| 6 | 5.76 | 6.24 | – | – | – | – |
| (7) | 6.71 | 7.29 | – | – | – | – |
| 8 | 7.71 | 8.29 | – | – | – | – |
| (9) | 8.71 | 9.29 | – | – | – | – |
| 10 | 9.71 | 10.29 | 9.25 | 10.75 | 9.25 | 10.75 |
| (11) | 10.65 | 11.35 | 10.10 | 11.90 | 10.10 | 11.90 |
| 12 | 11.65 | 12.35 | 11.10 | 12.90 | 11.10 | 12.90 |
| (14) | 13.65 | 14.35 | 13.10 | 14.90 | 13.10 | 14.90 |
| 16 | 15.65 | 16.35 | 15.10 | 16.90 | 15.10 | 16.90 |
| (18) | 17.65 | 18.35 | 17.10 | 18.90 | 17.10 | 18.90 |
| 20 | 19.58 | 20.42 | 18.95 | 21.05 | 18.95 | 21.05 |
| (22) | 21.58 | 22.42 | 20.95 | 23.05 | 20.95 | 23.05 |
| 25 | 24.58 | 25.42 | 23.95 | 26.05 | 23.95 | 26.05 |
| (28) | 27.58 | 28.42 | 26.95 | 29.05 | 26.95 | 29.05 |
| 30 | 29.58 | 30.42 | 28.95 | 31.05 | 28.95 | 31.05 |
| (32) | 31.50 | 32.50 | 30.75 | 33.25 | 30.75 | 33.25 |
| 35 | 34.50 | 35.50 | 33.75 | 36.25 | 33.75 | 36.25 |
| (38) | 37.50 | 38.50 | 36.75 | 39.25 | 36.75 | 39.25 |
| 40 | 39.50 | 40.50 | 38.75 | 41.25 | 38.75 | 41.25 |
| 45 | 44.50 | 45.50 | 43.75 | 46.25 | 43.75 | 46.25 |
| 50 | 49.50 | 50.50 | 48.75 | 51.25 | 48.75 | 51.25 |
| 55 | 54.40 | 55.60 | 53.50 | 56.50 | 53.50 | 56.50 |
| 60 | 59.40 | 60.60 | 58.50 | 61.50 | 58.50 | 61.50 |
| 65 | 64.40 | 65.60 | 63.50 | 66.50 | 63.50 | 66.50 |
| 70 | 69.40 | 70.60 | 68.50 | 71.50 | 68.50 | 71.50 |
| (75) | 74.40 | 75.60 | 73.50 | 76.50 | 73.50 | 76.50 |
| 80 | 79.40 | 80.60 | 78.50 | 81.50 | 78.50 | 81.50 |
| (85) | 84.30 | 85.70 | 83.25 | 86.75 | 83.25 | 86.75 |
| 90 | 89.30 | 90.70 | 88.25 | 91.75 | 88.25 | 91.75 |
| (95) | 94.30 | 95.70 | 93.25 | 96.75 | 93.25 | 96.75 |
| 100 | 99.30 | 100.70 | 98.25 | 101.75 | 98.25 | 101.75 |
| (105) | 104.30 | 105.70 | 103.25 | 106.75 | 103.25 | 106.75 |
| 110 | 109.30 | 110.70 | 108.25 | 111.75 | 108.25 | 111.75 |
| (115) | 114.30 | 115.70 | 113.25 | 116.75 | 113.25 | 116.75 |
| 120 | 119.30 | 120.70 | 118.25 | 121.75 | 118.25 | 121.75 |
| (125) | 124.20 | 125.80 | 123.00 | 127.00 | 123.00 | 127.00 |
| 130 | 129.20 | 130.80 | 128.00 | 132.00 | 128.00 | 132.00 |
| 140 | 139.20 | 140.80 | 138.00 | 142.00 | 138.00 | 142.00 |
| 150 | 149.20 | 150.80 | 148.00 | 152.00 | 148.00 | 152.00 |
| 160 | 159.20 | 160.80 | 158.00 | 162.00 | 158.00 | 162.00 |
| (170) | 169.20 | 170.80 | 168.00 | 172.00 | 166.00 | 174.00 |
| 180 | 179.20 | 180.80 | 178.00 | 182.00 | 176.00 | 184.00 |
| (190) | 189.10 | 190.90 | 187.70 | 192.30 | 185.40 | 194.60 |
| 200 | 199.10 | 200.90 | 197.70 | 202.30 | 195.40 | 204.60 |
| 220 | 219.10 | 220.90 | 217.70 | 222.30 | 215.40 | 224.60 |
| 240 | 239.10 | 240.90 | 237.70 | 242.30 | 235.40 | 244.60 |
| 260 | – | – | 257.40 | 262.60 | 254.80 | 265.20 |
| 280 | – | – | 277.40 | 282.60 | 274.80 | 285.20 |
| 300 | – | – | 297.40 | 302.60 | 294.80 | 305.20 |
| 320 | – | – | 317.15 | 322.85 | 314.30 | 325.70 |
| 340 | – | – | 337.15 | 342.85 | 334.30 | 345.70 |
| 360 | – | – | 357.15 | 362.85 | 354.30 | 365.70 |
| 380 | – | – | 377.15 | 382.85 | 374.30 | 385.70 |
| 400 | – | – | 397.15 | 402.85 | 394.30 | 405.70 |
| 420 | – | – | 416.85 | 423.15 | 413.70 | 426.30 |
| 440 | – | – | 436.85 | 443.15 | 433.70 | 446.30 |
| 460 | – | – | 456.85 | 463.15 | 453.70 | 466.30 |
| 480 | – | – | 476.85 | 483.15 | 473.70 | 486.30 |
| 500 | – | – | 496.85 | 503.15 | 493.70 | 506.30 |
Select lengths based on application requirements, prioritizing non-parenthesized values for optimal standardization.
Thread Length Standards
Thread lengths (b) for bolts, screws, and studs are specified in ISO 888:2012 and GB/T 3106-2016, representing the threaded portion for partial thread fasteners. The table below provides values for nominal diameters (d) from 1.6 mm to 160 mm, categorized by total length (l) ranges.
These standards ensure adequate thread engagement for secure fastening while minimizing material use. For calculations, use formulas where table values are not listed, and consider full threading if unthreaded shank is ≤ 0.5d.
| Nominal Diameter d (mm) | l ≤ 125 (mm) | 125 < l ≤ 200 (mm) | l > 200 (mm) |
|---|---|---|---|
| 1.6 | 9 | – | – |
| 2 | 10 | – | – |
| 2.5 | 11 | – | – |
| 3 | 12 | – | – |
| 4 | 14 | – | – |
| 5 | 16 | – | – |
| 6 | 18 | – | – |
| 8 | 22 | 28 | – |
| 10 | 26 | 32 | – |
| 12 | 30 | 36 | – |
| (14) | 34 | 40 | – |
| 16 | 38 | 44 | 57 |
| 18 | 42 | 48 | 61 |
| 20 | 46 | 52 | 65 |
| 22 | 50 | 56 | 69 |
| 24 | 54 | 60 | 73 |
| 27 | 60 | 66 | 79 |
| 30 | 66 | 72 | 85 |
| 33 | 72 | 78 | 91 |
| 36 | 78 | 84 | 97 |
| 39 | 84 | 90 | 103 |
| 42 | 90 | 96 | 109 |
| 45 | 96 | 102 | 115 |
| 48 | 102 | 108 | 121 |
| 52 | – | 116 | 129 |
| 56 | – | 124 | 137 |
| 60 | – | 132 | 145 |
| 64 | – | 140 | 153 |
| 68 | – | 148 | 161 |
| 72 | – | 156 | 169 |
| 76 | – | 164 | 177 |
| 80 | – | 172 | 185 |
| 85 | – | 182 | 195 |
| 90 | – | 192 | 205 |
| 95 | – | – | 215 |
| 100 | – | – | 225 |
| 105 | – | – | 235 |
| 110 | – | – | 245 |
| 115 | – | – | 255 |
| 120 | – | – | 265 |
| 125 | – | – | 275 |
| 130 | – | – | 285 |
| 140 | – | – | 305 |
| 150 | – | – | 325 |
| 160 | – | – | 345 |
Use these values to determine thread engagement, ensuring safety and efficiency in design.
Key Notes and Calculations
Essential considerations for applying these standards include:
- Calculate thread length b unless specified: For l ≤ 125 mm, b = 2d + 6 mm; for 125 mm < l ≤ 200 mm, b = 2d + 12 mm; for l > 200 mm, b = 2d + 25 mm.
- If unthreaded shank ≤ 0.5d, manufacture as fully threaded.
- Tolerances for thread length b per ISO 4759-1: For slotted or recessed screws and studs, +2P / 0 (where P is pitch).
- Avoid nominal lengths in parentheses for better standardization.
- These apply to ISO metric threads per ISO 68-1.
These notes guide precise manufacturing and selection, enhancing reliability in mechanical assemblies.
Foire aux questions (FAQ)
- What is the purpose of standardizing nominal lengths?
Standardization ensures interchangeability, simplifies design, and optimizes production, reducing costs and errors in assembly. - How do product grades A, B, C differ in tolerances?
Grade A has the tightest tolerances for precision; B offers balanced accuracy; C is more lenient for cost-sensitive applications. - When should fully threaded fasteners be used?
If calculations yield an unthreaded shank ≤ 0.5d, opt for full threading to maintain strength and simplicity. - Why avoid lengths in parentheses?
They are secondary preferences; prioritizing non-parenthesized lengths promotes consistency and availability. - How to calculate thread length for non-tabulated sizes?
Use formulas: b = 2d + 6 mm (l ≤ 125 mm), b = 2d + 12 mm (125 < l ≤ 200 mm), b = 2d + 25 mm (l > 200 mm). - What tolerances apply to thread lengths?
Per ISO 4759-1, for screws and studs with drives, tolerances ensure proper grip; for slotted types, +2P / 0.
