• Screws are the closest and most familiar mechanical component of everyday life, and generally do not have devices that do not use screws.
• The beginning of screws was made with a helix carved into a tree during the Roman era, and a spiral pump. (a device that transfers water from low to high part.)
• As the current screw specifications were developed in the UK Industrial Revolution, the machinery industry needed a large amount of bolts and nuts, so it investigated the screws produced by a number of screw manufacturers at that time and made the Whitworth screw specifications in 1841. This is the origin of the current screw specifications.

Whitworth screw

• Starting in Britain in 1834, it was abolished in 1948 with the appearance of the Unified screw, and it was disqualified from international standards in 1962 with the birth of the ISO screw.

ISO inch screws (Unified screws)

• The improved specification of Whitworth screw were used in many field after the Serras screws announcement, and was announced as SAE screws by the British Automobile Technology Association in 1918, and became known as American screws in 1938. Since then, with the aim of measuring the compatibility of arms-related screws, screw's agreements have been carried out in the United States, Britain and Canada, which were announced as unfied screws in 1948.

Metric screws

• The current prototype of the meter screw is called the SF screw, which was established in France in 1894. In 1898, this screws acquired an international reputation as SI screw by a meeting of representatives from France, Switzerland and Germany. In 1940, it announced the entire chain of meter screw as ISA meter screw with consent from a number of countries, including the Czech Republic, Denmark, Italy and the Soviet Union. Development was halted due to World War II, but ISO meter screw was announced in 1962 to carry out international standardization projects after the war.

• A screw that has the same ball is called a screw along this slope by wrapping an extremely numerous slant (winding line) in the cylinder using a slanted side.
  It is also a screw that uses a small force to move a large load by turning a straight motion into a rotary motion.

• Generally, there are two main types of terms that refer to screws. The main term is Japanese, Neji, English is interpreted in Korean, so it is called screws.
• The term implies that the Japanese Neji (Ne: twisting Ji: tool) means a tool for twisting, and in English they can be divided into two types: SCREW and THREAD. Screw has the comprehensive meaning of screws such as screw parts, screw products, etc. The thread refers to the screw itself (Triangular thread, Square thread, etc.)
• The terms and meanings of this education are THREAD and it is to understand this.

Screw

• A cylinder or whole cone with a screw thread.

Male Thread

• Screws with threads on the outer face of a cylinder or cone

Female Thread

• Screws with threads on the inside face of a cylinder or cone

Single screw

• Screws which lead and pitch are same

Double screw

• Screws which lead is same as a twice of pitch

Right hand thread

• A screw that moves away from the person when following a thread in the direction (right turn) of a clock.

Left hand thread

• A screw that moves away from the person when following a thread in the opposite direction (left-hand rotation) of a clock needle.

Screws component

• A part that has screws in its part, such as bolts, nuts, etc.

Flank

• It is usually straight as part of a straight line except for a straight line connecting the mountain peaks with the bottom of the core.

Mountain peaks

• the part that connects the flanks on each side of the thread.

Bottom of the core

• The side part that connects the flanks on both sides of the screw groove. There is in the innermost point for the male screw and in the deepest part for the female screw.

Angle of thread

• The angle of the two flanks measured in the axial section of the screw.

Angle of flank

• The angle at which the individual flanks measured in the axial cross section of the screw form a straight line perpendicular to the axis.

Pitch

• the distance measured parallel to the axle line at the two points of the thread adjacent to each other in the axial cross section of the screw.

Lead

• The distance to move the screw in the axial direction of the thread when it is rotated around its axis.

Angle of lead

• The angle that forms the tangent of the pitch diameter cylinder at right angles to the axis at the one point of the screw's helix and the above in relation

Full diameter

• Diameter of a hypothetical cylinder (or cone) that is tangent to the peak of a mountain of a male screw.

Minor diameter

• Diameter of a hypothetical cylinder (or cone) tangent to the peak of a female screw.

Core diameter of male screw

• Diameter of a hypothetical cylinder (or cone) tangential to the base of the bottom of core for male screw

Core diameter of female screw

• Diameter of a hypothetical cylinder (or cone) tangential to the base of the bottom of core for female screw

pitch diameter

• the diameter of a hypothetical cylinder (or cone) whose width of grooves between threads is equal to that of thread and width.

산의 높이

• 나사의 봉우리를 연결하는 직선과 골밑을 연결하는 직선과의 사이를 축선에서 직각으로측정한 거리.

Height of mountain

• The distance measured in a straight line between the imaginary cylinder tangent to the point of intersection by extending the flank of the screw in the direction of calculation and the virtual cylinder tangent to the point of intersection by extending it to the bottom of the core.

pitch screw part

• This refers to the effective part that can be used as a screw. Include a screw that is not safe from calculation (mountain peak) by means of chamfer.

Screw part

• The part of a male or female screw of a screw. However, in the case of a male screw with a cylinder, incomplete screws at the boundary between the cylinder and the complete screw are not included, and incomplete screws at the end of the screw are included in the screw. In a male screw parts of screw rod(the whole axle is a screw, without a cylinder), incomplete screws at the lower neck and end of the screw are included in the screw. In addition, the chamfer at the end of the screw is part of the incomplete thread.

Name of each part for screw

• Pitch : The distance from the tip of the thread to the end of the thread adjacent to it is called pitch.
• Pitch Diameter : The diameter of a virtual source whose width is equal to that of a thread and a core is called the pitch diameter.

Type of screw

• Metric Thread

  Mark the diameter and pitch in mm and indicate the size of the screw as pitch.
  The angle of the thread is 60 ̊, and the shape of the thread is flattened and the bottom of the core is rounded.

  • Metric coarse thread : M5 [M5*0.8]
  • Metric fine thread : M5*0.5
• Unified Thread

  Indicate the diameter in inches with an inch screw and the size of the screw is expressed with the number of threads between 1 inch.
  The thread has an angle of 60 ̊ and is similar in shape to the metric screw.

  • Unified coarse thread : 3/8-16UNC
  • Unified fine thread : 3/8-24UNF
  • Unified national extra fine thread : 1/4-32UNEF
• British pipe thread

  There are two types of taper screw and straight screw, which are used to connect piping tubes, and taper screws are 1/16 taper.
  The angle of the thread is 55 ̊, and the nomenclature method is in accordance with the nomenclature of gas pipe.

  • Taper screw : R1/8(Male screw), Rc1/4(Female screw)
  • Straight screw : G3/8
• American pipe thread

  The screw used to connect the pipe consists of a male screw and a female screw, with a taper screw 1/16 in shape.
  The angle of the thread is 60 ̊, and the nomenclature method is in accordance with the nomenclature of gas pipe.

  • Taper screw : NPT 1/8(Female screw. Male screw)
• Other screw
  • Cycle thread : BC3/4(General purpose), BC2.6(For sports)
  • Screw for sewing machine : SM1/4 40
  • Screw for electric bulb : E 10
  • Tire air valve screw : TV 8(For automobile use), CTV 8 산30(For bicycle use)