受到阻力时，螺纹产生轴向力的现象可由斜面原理来 解释。
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Further rotation demands increased efforts (torque), with a resulting increase in axial force.
再进一步旋转需要增加扭矩（torque）同时轴向力也 增大。
如标示：，表示：一外螺纹零件，公称直径英寸，20 牙/英寸的统一粗牙螺纹，公差等级2，及右旋螺纹。
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Usually the hand designation is omitted for right-hand, since these are standard. Another example is 3/4-16UNF-2B-LH which designates an internal, left-hand thread having a basic major diameter of 3/4 in., and 16 unified fine threads per inch of length.
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The coarse-thread series (UNC) is most common and is recommended for general assembly use where vibration is not a problem and where frequent disassembly is required.
所有这些都是基于单头螺纹螺钉的，它是一个简单机 械，可以在最小的空间内产生很大的机械增益，而且 在理论上是自锁的。
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Effective use however, requires the aid of two other simple machines: the lever(手柄) and the wheel-and-axle machine. The wrench(扳手) is basically a lever, the screwdriver is a wheeland-axle machine.
统一标准超细牙螺纹用于薄壁零件的外螺纹配合。
This series is also more resistance to vibration and provides for very fine adjustment.
该系列用于要求抗振动性强的场合，及更精密调整的 场合。
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ISO标准包含许多直径螺距组合系列，但推荐的美国 标准指定了单一的直径螺距组合系列。
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Metric threads(公制螺纹) are designated by the letter M followed by basic major diameter(公称直径) in millimeters, which is then followed by the pitch in millimeters separated by the symbol “x”.
尽管存在其它先进的联接方式，螺纹紧固件的应用仍 保留了机器设计和制造过程中基本的装配方法。
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Thus the designers must select standard fasteners of the type and size that will most adequately suit the application at hand.
因此，设计者在满足使用要求时应用标准类型和尺寸 的螺纹紧固件。
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A threaded fastener is a device that can effectively exert(施加) and maintain a large force in one direction (axially) through the application of a small force in another direction (tangentially).
统一标准粗牙螺纹系列是最普通的，推荐用于一般的
装配场合——振动较小，频繁拆卸。
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The fine-thread series (UNF) is somewhat stronger in tension and is more suitable where fine adjustment may be required.
Matching external and internal threads so that they may be assembled is the key to all threaded fasteners.
螺纹也可在孔的内圆柱表面上生成，这就形成了螺母。 内外螺纹匹配是所有螺纹紧固件装配的关键。
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Threaded fasteners perform the function of locating, clamping, adjusting and transmitting force from one machine member to another.
螺纹紧固件起着定位、加紧、调整和从一个机器零 件向另一个传递力的作用。
This series is often used in aircraft assemblies.
统一标准细牙螺纹系列具有较大张紧力，较适用于精 密调整的场合。该系列常用于航空器的装配。
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The extra-fine-thread series (UNEF) is employed where the mating external thread is in a thin-walled member(薄壁件).
螺纹紧固件是这样一个装置，在切线方向上施加一个 较小的力，能在轴线方向上有效地产生并保持一个较 大的力。
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All are based on the single threaded screw, a simple machine that yields a large mechanical advantage(机械增益) in minimal space and theoretically is self locking(自锁的).
They are thoroughly standardized and generally designed for use in mass production of machines(设计用于机床大批量 生产).
它们已经完全标准化，且通常用于大批量生产的机 器上。
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The use of the threaded fasteners remains the basic assembly method in the design and construction of machines despite advances in other methods of joining.
上一课回顾
单词复习：
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Lesson 4 Threaded Fasteners
螺纹紧固件
重点词汇： 1.locate vt. 确定位置 2.clamp vt. 夹紧 3. Mass production 大规模生产 4. Screw/Bolt/Stud/Nut 5.torque 扭矩 6.washer n. 垫片 7.helical spring lockwasher 弹簧垫圈
Thus the connection remains tight unless some external influence such as vibration or temperature change overrides the initial condition.
这样只要没有像振动、温度变化这些外部因素改变初 始条件，这种联接就能维持紧固的状态。
统一标准螺纹用一个简化符号标识在图形零件的细表 等场合。该符号包括：尺寸，螺纹系列，配合等级， 内外螺纹符号（A——外螺纹，B——内螺纹）及旋向。
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For example, the designation 1/4-20UNC-2ARH identifies an externally threaded part having a basic major diameter of 1/4 in., unified coarse thread with 20 threads per inch, tolerance class 2, and right-hand threads.
螺纹紧固件是尺寸较小，承受高拉应力的零件。螺纹 是通过在圆柱形棒料上切削加工或冷压成型的沟槽形 成的螺旋凸起物，这样产生了大家所知的螺钉、螺栓、 双头螺柱。
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Threads are also formed internally in cylindrical holes and constitute(构成) what is known as a nut(螺母).
Unified standard threads are identified on drawings, parts lists(零件清单), and so forth, with a shorthand notation(简单标注法) that includes size, thread series, class of fit, external or internal thread symbol (A is for external threads, B is for internal threads), and the hand of thread(螺纹旋向).
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Unified standard thread is available in three basic series of diameter-pitch( 直 径 螺 距 ) combinations.