Selecting a correct screw require an understanding of how a screw head interact with a drive recess and how a screw head interact with a material. Many people encounters problems when a driver bit dont fit a screw head proper, and these problems cause the driver bit to slip inside a screw head. When a driver bit slips inside a screw head, the driver bit can strip the screw head and make the screw head useless.
Therefore, you must ensure that the driver bit match the specific size of the screw head to prevent stripping the screw head. The shape of a screw head determine how the screw head sit within a material. If you want a screw head to sit flush with a surface of a material, you must use a countersunk screw head.
How to Choose the Right Screw Head and Driver Bit
A countersunk screw head require a hole that match the angle of the countersunk screw head. For example, many woodworking application use an 82 degree angle for a countersunk screw head, but some metric standard use a 90 degree angle for a countersunk screw head. If you use an 82 degree countersunk screw head in a 90 degree hole, the screw head will sit more above the surface of the material.
This cause the screw head to create a bump on the surface of the material. Some screw heads is designed to sit above the surface of the material instead of sit flush with the surface. Raised screw heads, such as pan heads or truss heads, dont require you to drill a countersink hole because raised screw heads is designed to sit on top of the material.
A truss head provide a large bearing surface, and a large bearing surface is useful when you are fastening thin sheet metal because a large bearing surface prevent the screw head from pulling through the thin sheet metal. Other screw heads, such as button heads or socket cap screws, provide a low profile while allow you to apply high torque through a drive recess. The drive recess is the part of the screw head where the driver bit connect to the screw head.
A drive recess must be matched to the correct driver bit size so that the driver bit can transfer energy to the screw head. If a driver bit is too small for the drive recess, the driver bit will slip and create friction. This friction create heat and can damage the drive recess.
Torx drives use a six pointed star shape to create a drive recess, and Torx drives allow for higher torque transfer then Phillips drives. Phillips drives is designed to cam out, which means a Phillips drive is designed to slip to prevent over-tightening, but a Torx drive is designed to prevent slipping. The material you are fastening also determine which screw head you should use.
If you are fastening drywall, you should use a bugle head screw because a bugle head screw prevent the paper of the drywall from tearing. If you are performing structural work, you may need a hex head screw because a wrench can grip a hex head screw. You must also consider the width of the screw head because the screw heads width determine how close to the edge of a board you can place the screw.
If you place a screw too close to the edge of a board, the screw head may cause the board to split. Therefore, you must always match the screw head to the material and the driver bit to the drive recess.
