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Definition
| A screw thread is a helical ridge of uniform section running along the inside or outside of a cylinder or cone. |
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| Name 5 main uses for screw threads. |
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Definition
| 5 Main uses for screw threads are fastening, measurement, transmitting motion, multiplying force and sealing. |
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Term
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Definition
| The diameter at which the thickness of the thread equals the thickness of the space between the threads. It is approximately half way between the major and minor diameters. |
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Term
| What is the crest of a thread? |
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Definition
| It is the top of the helical ridge. The crest of an internal thread is on the minor diameter on an external thread it is the major diameter. (It is the part you can always touch with your finger) |
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Term
| What is the root of a thread? |
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Definition
| It is the bottom of the space between the threads. It is the major diameter on an internal thread and the minor diameter on an external thread. (It is the part you can not touch with your finger) |
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Term
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Definition
| Pitch is the distance from a point on one thread to the same point on the next thread. It is measured parallel to the axis of the part. |
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Term
| What is the flank of a thread? |
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Definition
| The angled side of a thread that connects the crest and root. |
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Term
| What is the lead of a thread? What is the lead of a multiple start thread? |
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Definition
| It is the axial distance a nut advances on a screw thread after one complete turn. It is equal to the pitch of the thread. The lead of a multiple start thread is equal to the pitch multiplied by the number of starts. |
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Term
| What are 5 Types of thread forms? What are their angles? Which two are the most common? |
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Definition
| Unified ISO(Metric) 60°, Square(National ACME/Brown & Sharpe) 29°, National Pipe/American Petroleum Institute 60° with a 3/4" taper per foot, American National 60°, British Whitworth 55°. The most common are Unified and ISO. In oil industries the American National Pipe thread is common. |
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Term
| What are square threads good for? Are they still common? |
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Definition
| Square threads are extremely strong and were used in machine parts to transit motion and force. They have been replaced in modern manufacturing by the acme thread form. |
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Term
| What is the tolerance position? The Tolerance grade? |
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Definition
| The tolerance position determines the allowance between mating parts. Defined by lower case letters e-h for external threads and uppercase letters G&H For internal threads. The later the letter the tighter the tolerance. The tolerance grade determines where the fit lies in the tolerance position. The larger the number the larger the tolerance from 1-9. |
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Term
| What is the three wire method? |
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Definition
| It is the method where you place three carefully chosen wires between the threads of a screw in such a way that the wires contact the pitch diameter of the screw. |
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