什么叫螺纹的大径小径?
一句话:牙顶叫大径,牙底叫小径——无论是内螺纹还是外螺纹。如下图所示(左为外螺纹,右为内螺纹):
至于中径,指大径与小径中间的值。
美制外螺纹(螺丝)的大径中径小径表
下表中螺纹规格采用美制常用规范如4-40UNC,但其它尺寸统一采用的单位为公制毫米MM:
外螺纹规格 |
公差等级 |
大径(外径) |
中径 |
小径 |
Max |
Min |
Max |
Min |
Max |
1-64UNC |
2A |
1.83896 |
1.74244 |
1.58242 |
1.53162 |
1.36652 |
3A |
1.8542 |
1.75768 |
1.59766 |
d |
1.38176 |
1-72UNF |
2A |
1.83896 |
1.75006 |
1.61036 |
1.5621 |
1.41986 |
3A |
1.8542 |
1.7653 |
1.6256 |
1.59004 |
1.4351 |
2-56UNC |
2A |
2.16916 |
2.06502 |
1.87452 |
1.82118 |
1.63068 |
3A |
2.1844 |
2.08026 |
1.88976 |
1.84912 |
1.64592 |
2-64UNF |
2A |
2.16916 |
2.07264 |
1.91262 |
1.86182 |
1.69672 |
3A |
2.1844 |
2.08788 |
1.92786 |
1.88976 |
1.71196 |
3-48UNC |
2A |
2.49682 |
2.38252 |
2.15392 |
2.0955 |
1.86436 |
3A |
2.5146 |
2.4003 |
2.1717 |
2.12852 |
1.88214 |
3-56UNF |
2A |
2.49682 |
2.39268 |
2.20218 |
2.1463 |
1.95834 |
3A |
2.5146 |
2.41046 |
2.21996 |
2.17932 |
1.97612 |
4-40UNC |
2A |
2.82448 |
2.69494 |
2.413 |
2.3495 |
2.06756 |
3A |
2.8448 |
2.71526 |
2.43332 |
2.38506 |
2.08788 |
4-48UNF |
2A |
2.82702 |
2.71272 |
2.48412 |
2.42316 |
2.19456 |
3A |
2.8448 |
2.7305 |
2.5019 |
2.45618 |
2.21234 |
5-40UNC |
2A |
3.15468 |
3.02514 |
2.7432 |
2.67716 |
2.39776 |
3A |
3.175 |
3.04546 |
2.76352 |
2.71526 |
2.41808 |
5-44UNF |
2A |
3.15722 |
3.0353 |
2.7813 |
2.7178 |
2.46888 |
3A |
3.175 |
3.05308 |
2.79908 |
2.75082 |
2.48666 |
6-32UNC |
2A |
3.48488 |
3.33248 |
2.96926 |
2.89814 |
2.54 |
3A |
3.5052 |
3.3528 |
2.98958 |
2.93624 |
2.56032 |
6-40UNF |
2A |
3.48488 |
3.35534 |
3.0734 |
3.00736 |
2.72796 |
3A |
3.5052 |
3.37566 |
3.09372 |
3.04292 |
2.74828 |
8-32UNC |
2A |
4.14274 |
3.99034 |
3.62712 |
3.55346 |
3.19786 |
3A |
4.1656 |
4.0132 |
3.64998 |
3.5941 |
3.22072 |
8-36UNF |
2A |
4.14528 |
4.00558 |
3.68808 |
3.61696 |
3.30454 |
3A |
4.1656 |
4.0259 |
3.7084 |
3.65506 |
3.32486 |
10-24UNC |
2A |
4.8006 |
4.61772 |
4.11226 |
4.02844 |
3.54076 |
3A |
4.826 |
4.64312 |
4.13766 |
4.07416 |
3.56616 |
10-32UNF |
2A |
4.80314 |
4.65074 |
4.28752 |
4.21132 |
3.85826 |
3A |
4.826 |
4.6736 |
4.31038 |
4.25196 |
3.88112 |
12-24UNC |
2A |
5.461 |
5.27812 |
4.77266 |
4.6863 |
4.20116 |
3A |
5.4864 |
5.30352 |
4.79806 |
4.73202 |
4.22656 |
12-28UNF |
2A |
5.461 |
5.2959 |
4.87172 |
4.79044 |
4.37896 |
3A |
5.4864 |
5.3213 |
4.89712 |
4.83616 |
4.40436 |
1/4-20UNC |
1A |
6.32206 |
6.01218 |
5.49656 |
5.35432 |
4.81076 |
2A |
6.32206 |
6.11632 |
5.49656 |
5.40258 |
4.81076 |
3A |
6.35 |
6.14426 |
5.5245 |
5.45338 |
4.8387 |
1/4-28UNF |
1A |
6.3246 |
6.07568 |
5.73532 |
5.60832 |
5.24256 |
2A |
6.3246 |
6.1595 |
5.73532 |
5.6515 |
5.24256 |
3A |
6.35 |
6.1849 |
5.76072 |
5.69722 |
5.26796 |
5/16-18UNC |
1A |
7.90702 |
7.57428 |
6.99008 |
6.83514 |
6.22808 |
2A |
7.90702 |
7.68604 |
6.99008 |
6.88848 |
6.22808 |
3A |
7.9375 |
7.71652 |
7.02056 |
6.94436 |
6.25856 |
5/16-24 |
1A |
79095.6 |
7.63524 |
7.22122 |
7.08152 |
6.64972 |
2A |
7.90956 |
7.72668 |
7.22122 |
7.12724 |
6.64972 |
3A |
7.9375 |
7.75462 |
7.24916 |
7.18058 |
6.67766 |
3/8-16UNC |
1A |
9.49198 |
9.1313 |
8.46074 |
8.29564 |
7.59968 |
2A |
9.49198 |
9.25322 |
8.46074 |
8.34898 |
7.59968 |
3A |
9.525 |
9.28624 |
8.49376 |
8.40994 |
7.6327 |
3/8-24UNF |
1A |
9.49706 |
9.22274 |
8.80872 |
8.66394 |
8.23722 |
2A |
9.49706 |
9.31418 |
8.80872 |
8.7122 |
8.23722 |
3A |
9.525 |
9.34212 |
8.83666 |
8.763 |
8.26516 |
7/16-14UNC |
1A |
11.07694 |
10.68324 |
9.89838 |
9.71804 |
8.91794 |
2A |
11.07694 |
10.81532 |
9.89838 |
9.779 |
8.91794 |
3A |
11.1125 |
10.85088 |
9.93394 |
9.84504 |
8.9535 |
7/16-20UNF |
1A |
11.07948 |
10.7696 |
10.93978 |
10.0965 |
9.56818 |
2A |
11.07948 |
10.87374 |
10.93978 |
10.1473 |
9.56818 |
3A |
11.1125 |
10.90676 |
10.3124 |
10.20826 |
9.6012 |
1/2-13UNC |
1A |
12.6619 |
12.24788 |
11.3919 |
11.20394 |
10.25906 |
2A |
12.6619 |
12.38504 |
11.3919 |
11.2649 |
10.33526 |
3A |
12.7 |
12.42314 |
11.43 |
11.33602 |
10.37336 |
1/2-20UNF |
1A |
12.66698 |
12.3571 |
11.84148 |
11.67892 |
12.52728 |
2A |
12.66698 |
12.46124 |
11.84148 |
11.73226 |
12.52728 |
3A |
12.7 |
12.49426 |
11.8745 |
11.79322 |
11.19124 |
9/16-12UNC |
1A |
14.24686 |
13.80998 |
12.87272 |
12.6746 |
11.72718 |
2A |
14.24686 |
13.9573 |
12.87272 |
12.74064 |
11.72718 |
3A |
14.2875 |
13.99794 |
12.91336 |
12.8143 |
11.76782 |
9/16-18UNF |
1A |
14.25194 |
13.9192 |
13.335 |
13.16228 |
12.573 |
2A |
14.259814 |
14.03096 |
13.335 |
13.2207 |
12.573 |
3A |
14.2875 |
14.06652 |
13.37056 |
13.2842 |
12.60856 |
5/8-11UNC |
1A |
15.83436 |
15.37208 |
14.33576 |
14.12494 |
13.08608 |
2A |
15.83436 |
15.52702 |
14.33576 |
14.19606 |
13.08608 |
3A |
15.875 |
15.56766 |
14.3764 |
14.27226 |
13.12672 |
5/8-18UNF |
1A |
15.83944 |
15.5067 |
14.9225 |
14.7447 |
14.1605 |
2A |
15.83944 |
15.61846 |
14.9225 |
14.80312 |
14.1605 |
3A |
15.875 |
15.60322 |
14.95806 |
14.86916 |
14.19606 |
3/4-10UNC |
1A |
19.00428 |
18.51152 |
17.35328 |
17.12976 |
15.97914 |
2A |
19.00428 |
18.67662 |
17.35328 |
17.20342 |
15.97914 |
3A |
19.05 |
18.72234 |
17.399 |
17.28724 |
16.02486 |
3/4-16UNF |
1A |
19.0119 |
18.65122 |
17.98066 |
17.79016 |
17.1196 |
2A |
19.0119 |
18.77314 |
17.98066 |
17.85366 |
17.1196 |
3A |
19.05 |
18.81124 |
18.01876 |
17.92224 |
17.1577 |
7/8-9UNC |
1A |
22.17674 |
21.64842 |
20.34286 |
20.10156 |
18.81632 |
2A |
22.17674 |
21.82368 |
20.34286 |
20.18284 |
18.81632 |
3A |
22.225 |
21.87194 |
20.39112 |
20.27174 |
18.86458 |
7/8-14UNF |
1A |
22.18436 |
21.79066 |
21.0058 |
20.80006 |
20.02536 |
2A |
22.18436 |
21.92274 |
21.0058 |
20.86864 |
20.02536 |
3A |
22.225 |
21.96338 |
21.04644 |
20.9423 |
20.066 |
1-8UNC |
1A |
25.3492 |
24.7777 |
23.28672 |
23.03018 |
21.56968 |
2A |
25.3492 |
24.9682 |
23.28672 |
23.114 |
21.56968 |
3A |
25.4 |
25.019 |
23.33752 |
23.20798 |
21.62048 |
1-14UNF |
1A |
25.35682 |
24.96566 |
24.17826 |
23.9649 |
23.19528 |
2A |
25.35682 |
25.0952 |
24.17826 |
24.03602 |
23.19528 |
3A |
25.4 |
25.13838 |
24.22144 |
24.11476 |
23.23846 |
美制内螺纹(螺母)的大、中、小径
下表螺纹规格为美制规范,如2-56UNC,但尺寸为公制单位毫米:
内螺纹规格 |
大径(外径) |
中径 |
小径(底径) |
Min |
Min |
Max |
Min |
Max |
1-64UNC |
1.8542 |
1.59766 |
1.6637 |
1.42494 |
1.58242 |
1.8542 |
1.59766 |
1.64592 |
1.42494 |
1.58242 |
1-72UNF |
1.8542 |
1.6256 |
1.6891 |
1.4732 |
1.6129 |
1.8542 |
1.6256 |
1.67386 |
1.4732 |
1.6129 |
2-56UNC |
2.1844 |
1.88976 |
1.96088 |
1.69418 |
1.87198 |
2.1844 |
1.88976 |
1.9431 |
1.69418 |
1.87198 |
2-64UNF |
2.1844 |
1.92786 |
1.99644 |
1.75514 |
1.91262 |
2.1844 |
1.92786 |
1.97866 |
1.75514 |
1.91262 |
3-48UNC |
2.5146 |
2.1717 |
2.2479 |
1.94056 |
2.1463 |
2.5146 |
2.1717 |
2.22758 |
1.94056 |
2.1463 |
3-56UNF |
2.5146 |
2.21996 |
2.29108 |
2.02438 |
2.1971 |
2.5146 |
2.21996 |
2.2733 |
2.02438 |
2.1971 |
4-40UNC |
2.8448 |
2.43332 |
2.51714 |
2.15646 |
2.38506 |
2.8448 |
2.43332 |
2.49428 |
2.15646 |
2.38506 |
4-48UNF |
2.8448 |
2.5019 |
2.58064 |
2.27076 |
2.45872 |
2.8448 |
2.5019 |
2.56032 |
2.27076 |
2.45872 |
5-40UNC |
3.175 |
2.76352 |
2.84734 |
2.48666 |
2.69748 |
3.175 |
2.76352 |
2.82702 |
2.48666 |
2.69748 |
5-44UNF |
3.175 |
2.79908 |
2.88036 |
2.55016 |
2.74066 |
3.175 |
2.54508 |
2.86004 |
2.55016 |
2.74066 |
6-32UNC |
3.5052 |
2.98958 |
3.08356 |
2.6416 |
2.8956 |
3.5052 |
2.98958 |
3.05816 |
2.6416 |
2.8956 |
6-40UNF |
3.5052 |
3.09372 |
3.18008 |
2.8194 |
3.0226 |
3.5052 |
3.09372 |
3.15722 |
2.8194 |
3.01244 |
8-32UNC |
4.1656 |
3.64998 |
3.7465 |
3.302 |
3.5306 |
4.1656 |
3.64998 |
3.7211 |
3.302 |
3.52806 |
8-36UNF |
4.1656 |
3.7084 |
3.79984 |
3.4036 |
3.6068 |
4.1656 |
3.7084 |
3.77698 |
3.4036 |
3.59664 |
10-24UNC |
4.826 |
4.13766 |
4.24688 |
3.683 |
3.9624 |
4.826 |
4.13766 |
4.21894 |
3.683 |
3.9497 |
10-32UNF |
4.826 |
4.31038 |
4.40944 |
3.9624 |
4.1656 |
4.826 |
4.31038 |
4.38404 |
3.9624 |
4.16814 |
12-24UNC |
5.4864 |
4.79806 |
4.90982 |
4.3434 |
4.5974 |
5.4864 |
4.79806 |
4.88188 |
4.3434 |
4.58978 |
12-28UNF |
5.4864 |
4.89712 |
5.0038 |
4.4958 |
4.7244 |
5.4864 |
4.89712 |
4.97586 |
4.4958 |
4.71678 |
1/4-20UNC |
6.35 |
5.5245 |
5.70992 |
4.9784 |
5.2578 |
6.35 |
5.5245 |
5.64896 |
4.9784 |
5.2578 |
6.35 |
5.5245 |
5.61594 |
4.9784 |
5.25018 |
1/4-28UNF |
6.35 |
5.76072 |
5.92582 |
5.3594 |
5.588 |
6.35 |
6.82752 |
5.86994 |
5.3594 |
5.588 |
6.35 |
6.82752 |
5.842 |
5.3594 |
5.5626 |
5/16-18UNC |
7.9375 |
7.02056 |
7.22122 |
6.4008 |
6.731 |
7.9375 |
7.02056 |
7.15518 |
6.4008 |
6.731 |
7.9375 |
7.02056 |
7.11962 |
6.4008 |
6.6802 |
5/16-24 |
7.9375 |
7.24916 |
7.4295 |
6.7818 |
7.0358 |
7.9375 |
7.24916 |
7.37108 |
6.7818 |
7.0358 |
7.9375 |
7.24916 |
7.3406 |
6.7818 |
6.99516 |
3/8-16UNC |
9.525 |
8.49376 |
8.70966 |
7.7978 |
8.1534 |
9.525 |
8.49376 |
8.63854 |
7.7978 |
8.1534 |
9.525 |
8.49376 |
8.60298 |
7.7978 |
8.08228 |
3/8-24UNF |
9.525 |
8.83666 |
8.83666 |
8.382 |
8.636 |
9.525 |
8.83666 |
8.96112 |
8.382 |
8.636 |
9.525 |
8.83666 |
8.513064 |
8.382 |
9.4488 |
7/16-14UNC |
11.1125 |
9.93394 |
10.16762 |
9.144 |
9.5504 |
11.1125 |
9.93394 |
10.08888 |
9.144 |
9.5504 |
11.1125 |
9.93394 |
10.05078 |
9.144 |
9.44118 |
7/16-20UNF |
11.06678 |
10.287 |
10.49274 |
9.7282 |
10.033 |
11.06678 |
10.287 |
10.42416 |
9.7282 |
10.033 |
11.06678 |
10.287 |
10.39114 |
9.7282 |
9.94664 |
1/2-13UNC |
12.7 |
11.43 |
11.67638 |
10.5918 |
11.0236 |
12.7 |
11.43 |
11.5951 |
10.5918 |
11.0236 |
12.7 |
11.43 |
11.55192 |
10.5918 |
10.88136 |
1/2-20UNF |
12.7 |
11.8745 |
12.08786 |
11.3284 |
11.6078 |
12.7 |
11.8745 |
12.01674 |
11.3284 |
11.6078 |
12.7 |
11.8745 |
11.98118 |
11.3284 |
11.52398 |
9/16-12UNC |
14.2875 |
12.91336 |
13.17244 |
11.9888 |
12.446 |
14.2875 |
12.91336 |
14.008608 |
11.9888 |
12.446 |
14.2875 |
12.91336 |
13.04544 |
11.9888 |
12.30122 |
9/16-18UNF |
14.2875 |
13.37056 |
13.59662 |
12.7508 |
13.081 |
14.2875 |
13.37056 |
13.52042 |
12.7508 |
13.081 |
14.2875 |
13.37056 |
13.48232 |
12.7508 |
12.96924 |
5/8-11UNC |
15.875 |
14.3764 |
14.64818 |
13.3858 |
13.8684 |
15.875 |
14.3764 |
14.55928 |
13.3858 |
13.8684 |
15.875 |
14.3764 |
14.51356 |
13.3858 |
13.69314 |
5/8-18UNF |
15.875 |
14.95806 |
15.1892 |
14.351 |
14.6812 |
15.875 |
14.95806 |
15.11046 |
14.351 |
14.6812 |
15.875 |
14.95806 |
15.07236 |
14.351 |
14.5542 |
3/4-10UNC |
19.05 |
17.399 |
17.6911 |
16.3068 |
16.8402 |
19.05 |
17.399 |
17.59458 |
16.3068 |
16.8402 |
19.05 |
17.399 |
17.54378 |
16.3068 |
16.6243 |
3/4-16UNF |
19.05 |
18.01876 |
18.26768 |
17.3228 |
17.6784 |
19.05 |
18.01876 |
18.18386 |
17.3228 |
17.6784 |
19.05 |
18.01876 |
18.14322 |
17.3228 |
17.54632 |
7/8-9UNC |
22.225 |
20.84832 |
20.70354 |
19.177 |
19.7612 |
22.225 |
20.84832 |
20.5994 |
19.177 |
19.7612 |
22.225 |
20.84832 |
20.54606 |
19.177 |
19.50974 |
7/8-14UNF |
22.225 |
21.04644 |
21.31568 |
20.2692 |
20.6756 |
22.225 |
21.04644 |
21.22424 |
20.2692 |
20.6756 |
22.225 |
21.04644 |
21.18106 |
20.2692 |
20.49272 |
1-8UNC |
25.4 |
23.33752 |
23.6728 |
21.971 |
22.606 |
25.4 |
23.33752 |
23.56104 |
21.971 |
22.606 |
25.4 |
23.33752 |
23.50516 |
21.971 |
22.34438 |
1-14UNF |
25.4 |
24.22144 |
24.4983 |
23.4442 |
23.8252 |
25.4 |
24.22144 |
24.40686 |
23.4442 |
23.8252 |
25.4 |
24.22144 |
24.3586 |
23.4442 |
23.6601 |
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