SCREW

Abstract

A screw includes a head, a rod extending from a lower end of the head and a tapered drilling portion extending from a lowest end of the rod; the rod having a normal thread with a predetermined length; the normal thread extending from a lower end of the head to the tapered drilling portion, but having a predetermined distance from a tip end of the tapered drilling portion; an umbrella thread extending from a lower end of the normal thread to the tip end of the tapered drilling portion; the umbrella thread being formed by an upper thread surface and a lower thread surface. A second angle between the upper thread surface of the normal thread and the lower thread surface of the normal thread becomes larger and larger from the end near the normal thread to an end near the tip end.

Claims

1. A screw comprising: a head (11), a rod (12) extending from a lower end of the head (11) and a tapered drilling portion (13) extending from a lowest end of the rod (12); the rod (12) having a normal thread (2) with a predetermined length; the normal thread (2) extending from a lower end of the head (11) to the tapered drilling portion (13), but having a predetermined distance from a tip end (131) of the tapered drilling portion (13); an umbrella thread (13) extending from a lower end of the normal thread (2) to the tip end (131) of the tapered drilling portion (13); the umbrella thread (13) being formed by an upper thread surface (2A) and a lower thread surface (2B); wherein a second angle between the upper thread surface (2A) of the normal thread (2) and the lower thread surface (2B) of the normal thread (2) becomes larger and larger from the end near the normal thread (2) to an end near the tip end (131).

2. The screw as claimed in claim 1, wherein the normal thread (2) is formed by an upper thread surface (2A) and a lower thread surface (2B); a first angle between the upper thread surface (2A) of the normal thread (2) and the lower thread surface (2B) of the normal thread (2) is smaller than 90 degrees.

3. The screw as claimed in claim 2, wherein the second angle between the upper thread surface (2A) of the normal thread (2) and the lower thread surface (2B) of the normal thread (2) is smaller than 90 degrees at an end near the normal thread (2); and at the end near the tip end (131), the second angle is greater than 90 degrees, while a slope of the upper surface (2A) of the umbrella thread (13 with respective to an axle of the tapered drilling portion (13) is unchanged.

4. The screw as claimed in claim 1, wherein there is another normal thread (2) which is parallel arranged with the normal thread (2), and there is another umbrella thread (13) which is parallel arranged with the umbrella thread (13).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 shows the embodiment of the present invention.

[0010] FIG. 2 is an enlarged cross section view of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] In order that those skilled in the art can further understand the present invention, a description will be provided in the following in details.

[0012] However, these descriptions and the appended drawings are only used to cause those skilled in the art to understand the objects, features, and characteristics of the present invention, but not to be used to confine the scope and spirit of the present invention defined in the appended claims. With reference to FIGS. 1 and 2, the structure of the present invention is illustrated. The screw 1 of the present invention includes a head 11, a rod 12 extending from a lower end of the head 11 and a tapered drilling portion 13 extending from a lowest end of the rod 12. The rod 12 has a normal thread 2 with a predetermined length. The normal thread 2 extends from the head 11 to the tapered drilling portion 13, but has a predetermined distance from a tip end 131 of the tapered drilling portion 13. The normal thread 2 is formed by an upper thread surface 2A and a lower thread surface 2B. A first angle between the upper thread surface 2A of the normal thread 2 and the lower thread surface 2B of the normal thread 2 is smaller than 90 degrees.

[0013] As illustrated in the drawing, an umbrella thread 13 extends from a lower end of the normal thread 2 to the tip end 131 of the tapered drilling portion 13. The umbrella thread 13 is formed by an upper thread surface 2A and a lower thread surface 2B. a second angle between the upper thread surface 2A of the normal thread 2 and the lower thread surface 2B of the normal thread 2 is smaller than 90 degrees at an end of the umbrella thread 13 near the normal thread 2, and the second end become larger and larger from the end near the normal thread 2 to an end near the tip end 131. At the end near the tip end 131, the second angle is greater than 90 degrees, while a slope of the upper surface 2A of the umbrella thread 13 with respect to an axle of the tapered drilling portion 13 is unchanged.

[0014] In another example, there is another normal thread 2 which is parallel arranged with the normal thread 2, and there is another umbrella thread 13 which is parallel arranged with the umbrella thread 13

[0015] From above said structure, it is known that the structure of the screw is easily in manufacturing. The tip end of the screw has a uniform structure. Furthermore in drilling, the screw has a uniform speed and is quick in drilling operation.

[0016] The present invention is thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.