The six-pointed star bit, most commonly referred to as a Torx bit, is available in a variety of sizes, and is most often used on machine screws. They're rarely used for wood screws, but even so, it's a good idea to have a set of both Torx bits and Torx screwdrivers readily available in your wood shop.
Torx or star screws are becoming more popular in a variety of applications, and as such, you're likely to run into a task sooner or later where you'll regret not having the right size in your tool chest.
What are the Advantages of Torx Screws?:
Torx screws are being used more regularly because they slip less than Phillips-head screws. It is interesting to note that Phillips-head screws are designed to slip. Until recent years, torque clutches on industrial power drills used in manufacturing weren't accurate enough, which lent to over-torquing of the screws, which could cause a number of failures in a manufacturing process. To compensate, Phillips-head screws were designed so that once torque reached a certain limit, the head would likely slip. While this caused some stripping of the screws and broken bits, it prevented over-torquing.
Now that torque clutches are far more accurate, it makes sense to to employ a screw/bit combination that is less likely to slip under heavy torque conditions. Enter Torx screws. Because of their design, a Torx bit can apply much greater torque to a screw without slippage, and since the clutch allows the machining operator to control the torque precisely, the Torx screw becomes a more reliable option than the Phillips. Because there is less slippage with a Torx than a Phillips, fewer bits are broken in the manufacturing process.
How Does This Apply to Woodworking?:
While there still aren't many Torx-head wood screws as of today, a great number of woodworking tools are built using Torx screws. If you need to do any maintenance on your woodworking tools or accessories, it would be highly-advisable to have a set of both Torx bits and Torx screwdrivers in your woodshop. It wouldn't surprise me to see more and more wood screws using Torx bits in the future, considering the improvements in cordless drill clutches in recent years.
Torx Bit Sizing:
Torx bits and screwdrivers typically come in a variety of sizes, or sets containing an assortment. The most common sizes used in manufacturing are T10, T15, T20, T25 and T30.