Choosing the right screw for the job
Selecting the right screws for your project can be confusing, especially when instructions start referring to pan head, round head, drywall and chipboard screws. Here on Home-Dzine we try to keep it simple and use screws that you will find at your local Builders Warehouse.
Even having said that, there is still a lot of confusion as to what screw to use for a particular project, So let's take a look at the most common screws and how you would apply these to your projects:
The screw that you will use the most is a cut screw. A cut screw has a smooth shank at the top (no thread) and when joining boards together, the smooth shank serves to pull the back board tightly to the front board. On Home-Dzine we don't always use wood glue on our projects and using a smooth shank screw ensures a tight join without the need for glue.
Cut screws have a square-drive head and every pack you buy will have a square bit included. Make sure that you use the exact square-drive bit for the screw you are using. If the bit is slightly smaller, you will soon end up with a stripped screw head. Although the cut screw has a cutting edge at the tip, a pilot hole is still necessary when joining board edges of 12mm up to 18mm thick. If you don't drill a pilot hole, chances are the board will split, even with a small diameter screw.
Because chipboard is not a solid board and has a tendency to crumble, chipboard screws are designed to provide more grip for the screw. Chipboard screws have a pozi-driv head and you will use the right-sized pozi bit 'PZ' for the screw size. For screws 3.5 to 5mm, a PZ2 is the correct PZ bit to use.
Zinc-plated chipboard screws for smaller projects are available in sizes from 3.0 x 16mm up to 4.0 x 20mm. These screws have a full thread, since they are intended for general fastening of hinges, brackets and hooks, and not for joining pieces together. These screws also have a pozi-driv head and will use a PZ2 bit.
NOTE: All the above screws have a countersink head, which means that you need to use a countersink bit in hardwood and boards to ensure that the screw head sits flush or just below the surface of the material you are using.