Table 3. Standard Series and Selected Combinations—Unified Screw Threads Table 3. (Continued) Standard Series and Selected Combinations—Unified Screw Threads
External b
Internal b
Nominal Size, Threads per Inch, and Series Designation a 1 1 ∕ 4 -12 UNF
Major Diameter
UNR Minor Dia., c Max (Ref.)
Major Diameter
Pitch Diameter
Minor Diameter
Pitch Diameter
Allow ance
Max d
Min e
Max d
Class
Min
Min
Min
Max
Min
Max
Min 1.2500 1.2500 1.2500 1.2500 1.2500 1.2500 1.2500 1.2500 1.2500 1.2500 1.2500 1.2500 1.2500 1.3125 1.3125 1.3125 1.3125 1.3125 1.3125 1.3125 1.3125 1.3125 1.3125 1.3125 1.3125 1.3750 1.3750 1.3750
Class
1A 0.0018 1.2482 1.2310 2A 0.0018 1.2482 1.2368 3A 0.0000 1.2500 1.2386 2A 0.0016 1.2484 1.2381 2A 0.0015 1.2485 1.2391 3A 0.0000 1.2500 1.2406 2A 0.0015 1.2485 1.2398 3A 0.0000 1.2500 1.2413 2A 0.0014 1.2486 1.2405 3A 0.0000 1.2500 1.2419 2A 0.0013 1.2487 1.2415 2A 0.0012 1.2488 1.2423 3A 0.0000 1.2500 1.2435 2A 0.0021 1.3104 1.2954 3A 0.0000 1.3125 1.2975 2A 0.0017 1.3108 1.2994 3A 0.0000 1.3125 1.3011 2A 0.0015 1.3110 1.3016 3A 0.0000 1.3125 1.3031 2A 0.0015 1.3110 1.3023 3A 0.0000 1.3125 1.3038 2A 0.0014 1.3111 1.3030 3A 0.0000 1.3125 1.3044 2A 0.0012 1.3113 1.3048 3A 0.0000 1.3125 1.3060 1A 0.0024 1.3726 1.3453
— 1.1941 1.1849 — 1.1941 1.1879 — 1.1959 1.1913 — 1.2020 1.1966 — 1.2079 1.2028 — 1.2094 1.2056 — 1.2124 1.2075 — 1.2139 1.2103 — 1.2161 1.2114 — 1.2175 1.2140 — 1.2216 1.2173 — 1.2256 1.2215 — 1.2268 1.2237 — 1.2292 1.2221 — 1.2313 1.2260 — 1.2567 1.2509 — 1.2584 1.2540 — 1.2704 1.2653 — 1.2719 1.2681 — 1.2749 1.2700 — 1.2764 1.2727 — 1.2786 1.2739 — 1.2800 1.2765 — 1.2881 1.2840 — 1.2893 1.2862 — 1.2643 1.2523
1.1490 1.1490 1.1508 1.1633 1.1741 1.1756 1.1823 1.1838 1.1891 1.1905 1.1991 1.2063 1.2075 1.1616 1.1637 1.2116 1.2133 1.2366 1.2381 1.2448 1.2463 1.2516 1.2530 1.2688 1.2700 1.1741 1.1741 1.1765
1B 1.160 2B 1.160 2B 1.173 2B 1.182
1.178 1.178 1.188 1.196
1.1959 1.2079 1.1959 1.2039 1.1959 1.2019 1.2036 1.2106 1.2094 1.2160 1.2094 1.2144 1.2139 1.2202 1.2139 1.2186 1.2175 1.2236 1.2175 1.2220 1.2229 1.2285 1.2268 1.2321 1.2268 1.2308 1.2313 1.2405 1.2313 1.2382 1.2584 1.2659 1.2584 1.2641 1.2719 1.2786 1.2719 1.2769 1.2764 1.2828 1.2764 1.2812 1.2800 1.2861 1.2800 1.2846 1.2893 1.2947 1.2893 1.2933 1.2667 1.2822 1.2667 1.2771 1.2667 1.2745
3B 1.1600 1.1698
1 1 ∕ 4 -14 UNS 1 1 ∕ 4 -16 UN
3B 1.1820 1.1909
2B 1.190
1.203
1 1 ∕ 4 -18 UNEF
3B 1.1900 1.1980
2B 1.196
1.207
1 1 ∕ 4 -20 UN
3B 1.1960 1.2036
2B 1.205 2B 1.211
1.215 1.220
1 1 ∕ 4 -24 UNS 1 1 ∕ 4 -28 UN
3B 1.2110 1.2176
2B 1.177
1.202
1 5 ∕ 16 -8 UN
3B 1.1770 1.1922
2B 1.222
1.240
1 5 ∕ 16 -12 UN
3B 1.2220 1.2323
2B 1.245
1.259
1 5 ∕ 16 -16 UN
3B 1.2450 1.2534
2B 1.252
1.265
1 5 ∕ 16 -18 UNEF
3B 1.2520 1.2605
2B 1.258
1.270
1 5 ∕ 16 -20 UN
3B 1.2580 1.2661
2B 1.274
1.282
1 5 ∕ 16 -28 UN
3B 1.2740 1.2801
1B 1.195 2B 1.195
1.225 1.225
1 3 ∕ 8 -6 UNC
2A 0.0024 1.3726 1.3544 1.3453 1.2643 1.2563
3A 0.0000 1.3750 1.3568
— 1.2667 1.2607
3B 1.1950 1.2146
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