1、加大螺丝与机器的接触面积。
2、消除弹簧垫在卸螺丝的时候对机器表面的损害。使用时必须是一弹簧垫一平垫，平垫挨着机器表面，弹簧垫在平垫和螺帽之间。
平垫的标准
各国的标准都不一样。
下面是美国的平垫标准:
规 格 Specification | 内径公差 Minor Diameter | 外径公差 Outside Diameter | 厚度公差 Thickness Tolerance | 厚度公差分解 Thickness Tolerance Disintegration |
USS 3/16 | 6.22~6.73 | 14.15~14.66 | 0.91~1.65 | 0.91~1.40 |
1.40~1.65 | ||||
USS 1/4 | 7.80~8.31 | 18.47~19.02 | 1.30~2.03 | 1.30~1.65 |
1.65~2.03 | ||||
USS 5/16 | 9.40~9.91 | 22.05~22.99 | 1.63~2.64 | 1.63~2.20 |
2.20~2.64 | ||||
USS 3/8 | 11.00~11.51 | 25.22~26.16 | 1.63~2.64 | 1.63~2.20 |
2.20~2.64 | ||||
USS 7/16 | 12.57~13.08 | 31.57~32.51 | 1.63~2.64 | 1.63~2.20 |
2.20~2.64 | ||||
USS 1/2 | 14.15~14.60 | 34.75~35.69 | 2.18~3.35 | 2.18~2.70 |
2.70~3.00 | ||||
3.00~3.35 | ||||
USS 9/16 | 15.75~16.26 | 37.13~38.07 | 2.18~3.35 | 2.18~2.70 |
2.70~3.00 | ||||
3.00~3.35 | ||||
USS 5/8 | 17.30~18.24 | 44.27~45.21 | 2.74~4.06 | 2.74~3.20 |
3.20~3.60 | ||||
3.60~4.06 | ||||
USS 3/4 | 20.45~21.39 | 50.62~51.56 | 3.10~4.50 | 3.10~3.60 |
3.60~4.20 | ||||
4.20~4.50 | ||||
USS 7/8 | 23.65~24.58 | 56.97~57.91 | 3.45~4.88 | 3.45~4.00 |
4.00~4.30 | ||||
4.30~4.88 | ||||
USS 1 | 26.80~27.74 | 63.32~64.26 | 3.45~4.88 | 3.45~4.00 |
4.00~4.30 | ||||
4.30~4.88 | ||||
USS 11/8 | 31.57~32.51 | 69.67~70.61 | 3.45~4.88 | 3.45~4.00 |
4.00~4.30 | ||||
4.30~4.88 | ||||
USS 11/4 | 34.75~35.69 | 76.02~76.96 | 3.45~4.88 | 3.45~4.00 |
4.00~4.30 | ||||
4.30~4.88 | ||||
USS 13/8 | 37.85~39.24 | 82.30~83.69 | 3.89~5.41 | 3.89~4.40 |
4.40~5.00 | ||||
5.00~5.41 | ||||
USS 11/2 | 41.02~42.42 | 88.65~90.04 | 3.89~5.41 | 3.89~4.40 |
4.40~5.00 | ||||
5.00~5.41 | ||||
USS 15/8 | 44.20~45.59 | 95.00~96.39 | 3.89~5.41 | 3.89~4.40 |
4.40~5.00 | ||||
5.00~5.41 | ||||
USS 13/4 | 47.37~48.77 | 101.35~102.74 | 3.89~5.41 | 3.89~4.40 |
4.40~5.00 | ||||
5.00~5.41 | ||||
USS 17/8 | 50.55~51.04 | 107.70~109.09 | 3.89~5.41 | 3.89~4.40 |
4.40~5.00 | ||||
5.00~5.41 | ||||
USS 2 | 53.72~55.12 | 114.05~115.44 | 3.89~5.41 | 3.89~4.40 |
4.40~5.00 | ||||
5.00~5.41 |
