Screw for use in concrete

Abstract

The concrete screw of the invention reduces the driving torque required, reduces shear failure, and provides increased pull-out resistance The screw has Hi-Low threads, the major thread being of greater diameter than the minor thread, the threads having a pitch displacement at least equal to the diameter of the screw shank Helical grooves of opposite rotational hand from the threads extend the length of the threaded portion of the screw, and have a pitch displacement at least two times the diameter of the screw shank In a limited portion adjacent the tip of the screw, and extending generally no more than 1 / 3 of the length of the threads, are intermediate helical counter-rotation grooves The intermediate grooves may be adjacent the principal grooves to produce a W-shaped notch in the threads Preferably, the W-shaped notch is asymmetrical in the direction of rotation of the grooves.

Description

technical field [0001] The present invention generally relates to a screw fastener suitable for fastening in a hole drilled in a masonry structure such as concrete, although it may be used in other masonry materials such as brick or ceramics . This screw is of the type, sometimes referred to as a Hi-Lo (high-low screw), having a major thread with a large top diameter and a middle secondary thread with a small top diameter. Background technique [0002] Concrete screws—that is, screws suitable for use in concrete or other masonry structures—are usually screwed by hand or power tools into appropriately sized bore holes, where the diameter of the hole is slightly larger than the diameter of the shank of the screw, At the same time, the top diameter of the thread of the screw exceeds the diameter of the hole. [0003] Typically, the threads of the concrete screw cut into the sidewall of the hole. Heretofore, screws with a fine pitch have been used which allow convolution thre...

AI Technical Summary

Problems solved by technology

However, this screw configuration increases the risk of over-cutting into the sidewall and "drilling out" of the concrete due to over-torqued screws

In any case, the result of increasing the number of threads and the resulting length of the thread contacting the side wall is an increase in the resistance to rotation

Disadvantageously, many concrete screws suffer from this increased resistance whereby the torque required to screw the screw to the desired depth results in overtorque of the threads and shearing of the screw shaft

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