Patent ID: 9695859
Date: 2017-07-04
CPC Classifications: F16B

Claim:
1. A fastening bolt for use in concrete comprising: a shaft defining a central axis; a head disposed on a first end of said shaft; a drilling portion defined on a second end of said shaft opposite to said first end; a plurality of first threads spirally disposed on said shaft and extending from said drilling portion toward said head; and a plurality of second threads spirally disposed between said first threads, wherein an outer diameter of said second threads is smaller than an outer diameter of said first threads, one of said second threads being an unbroken second thread disposed toward the head of the shaft and uninterruptedly encircling the shaft at least once, a remainder of said second threads being broken second threads disposed toward the drilling portion of the shaft and having a plurality of recesses formed thereon; wherein each of said plurality of first threads has a trailing surface facing said head and a leading surface facing said drilling portion, said leading surface and said trailing surface converging on a thread ridge, said first thread defining a line which is perpendicular to said central axis of said shaft and passes said thread ridge, said leading surface being inclined to said line at a leading angle, said trailing surface being inclined to said line at a trailing angle, said trailing angle being smaller than said leading angle, one of said first threads being an unbroken first thread disposed toward the head of the shaft and uninterruptedly encircling the shaft at least once, a remainder of said first threads being broken first threads disposed toward the drilling portion of the shaft and having a plurality of cutting grooves formed thereon, each of said plurality of cutting grooves being formed by walls with different lengths and being opened at an angle, said angle being not over 90 degrees, each of said plurality of cutting grooves being opened in a direction opposite to a screwing direction of said shaft.