Machinery's Handbook, 31st Edition
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Interference-Fit Threads Table 1. External Thread Dimensions for Class 5 Interference-Fit Threads ANSI/ASME B1.12-1987 (R2018)
Major Diameter, Inches NC-5 CSF for driving in brass and ferrous material with hardness equal to or less than 160 BHN L e = 1 1 ∕ 4 Diam.
NC-5 HF for driving in ferrous material with hardness greater than 160 BHN L e = 1 1 ∕ 4 Diam.
NC-5 ONF for driving in nonferrous except brass (any hardness) L e = 2 1 ∕ 2 Diam.
Pitch Diameter, Inches
Minor Diameter, Inches
Nominal Size
Max Max 0.2500-20 0.2470 0.2418 0.2470 0.2418 0.2470 0.2418 0.2230 0.2204 0.1932 0.3125-18 0.3080 0.3020 0.3090 0.3030 0.3090 0.3030 0.2829 0.2799 0.2508 0.3750-16 0.3690 0.3626 0.3710 0.3646 0.3710 0.3646 0.3414 0.3382 0.3053 0.4375-14 0.4305 0.4233 0.4330 0.4258 0.4330 0.4258 0.3991 0.3955 0.3579 0.5000-13 0.4920 0.4846 0.4950 0.4876 0.4950 0.4876 0.4584 0.4547 0.4140 0.5625-12 0.5540 0.5460 0.5575 0.5495 0.5575 0.5495 0.5176 0.5136 0.4695 0.6250-11 0.6140 0.6056 0.6195 0.6111 0.6195 0.6111 0.5758 0.5716 0.5233 0.7500-10 0.7360 0.7270 0.7440 0.7350 0.7440 0.7350 0.6955 0.6910 0.6378 0.8750- 9 0.8600 0.8502 0.8685 0.8587 0.8685 0.8587 0.8144 0.8095 0.7503 1.0000- 8 0.9835 0.9727 0.9935 0.9827 0.9935 0.9827 0.9316 0.9262 0.8594 1.1250- 7 1.1070 1.0952 1.1180 1.1062 1.1180 1.1062 1.0465 1.0406 0.9640 1.2500- 7 1.2320 1.2200 1.2430 1.2312 1.2430 1.2312 1.1715 1.1656 1.0890 1.3750- 6 1.3560 1.3410 1.3680 1.3538 1.3680 1.3538 1.2839 1.2768 1.1877 1.5000- 6 1.4810 1.4670 1.4930 1.4788 1.4930 1.4788 1.4089 1.4018 1.3127 Based on external threaded members being steel ASTM A325 (SAE Grade 5) or better. L e = length of engagement. Table 2. Internal Thread Dimensions for Class 5 Interference-Fit Threads ANSI/ASME B1.12-1987 (R2018) Min Max Min Max Min Max Min
NC-5 IF Ferrous Material
NC-5 INF Nonferrous Material
Pitch Diameter
Major Diam.
Minor Diam. a
Minor Diam. a
Nominal Size 0.2500-20 0.3125-18 0.3750-16 0.4375-14 0.5000-13 0.5625-12 0.6250-11 0.7500-10 0.8750- 9 1.0000- 8 1.1250- 7 1.2500- 7 1.3750- 6 1.5000- 6
Tap Drill
Tap Drill
Min
Max 0.206 0.263 0.318 0.381 0.440 0.497 0.554 0.678 0.789 0.904 1.015 1.140 1.247 1.372
Min
Max 0.206 0.263 0.318 0.372 0.429 0.485 0.540 0.655 0.769 0.880 0.986 1.111 1.213 1.338
Min
Max
Min
0.196 0.252 0.307 0.374 0.431 0.488 0.544 0.667 0.777 0.890 1.000 1.125 1.229 1.354
0.2031 0.2610 0.3160 0.3750 0.4331 0.4921 0.5469 0.6719 0.7812 0.8906 1.0000 1.1250 1.2344 1.3594
0.196 0.252 0.307 0.360 0.417 0.472 0.527 0.642 0.755 0.865 0.970 1.095 1.195 1.320
0.2031 0.2175 0.2201 0.2532 0.2610 0.2764 0.2794 0.3161 0.3160 0.3344 0.3376 0.3790 0.3680 0.3911 0.3947 0.4421 0.4219 0.4500 0.4537 0.5050 0.4844 0.5084 0.5124 0.5679 0.5313 0.5660 0.5702 0.6309 0.6496 0.6850 0.6895 0.7565 0.7656 0.8028 0.8077 0.8822 0.8750 0.9188 0.9242 1.0081 0.9844 1.0322 1.0381 1.1343 1.1094 1.1572 1.1631 1.2593 1.2031 1.2667 1.2738 1.3858 1.3281 1.3917 1.3988 1.5108
a Fourth decimal place is 0 for all sizes. All dimensions are in inches, unless otherwise specified.
Externally Threaded Products: Points of externally threaded components should be chamfered or otherwise reduced to a diameter below the minimum minor diameter of the thread. The limits apply to bare or metallic coated parts. The threads should be free from excessive nicks, burrs, chips, grit or other extraneous material before driving.
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