The simplest of functions can be utterly botched–turning a screw, for example.

We're always told we should use the right-size tool for a given task. Those in the know advise us to use a screwdriver that fits perfectly into the slot in the screw. Because we got a chance to spend some time with expert recently, we learned why that's so important. The expert is a man who designs screws–John M. "Brad" Wagner, president of Grabber Screws. He is an engineer and entrepreneur whose high-end screw company is international.

How simple is his principle? According to Wagner, if you use the right-size tip, the full force of the blade is exerted against the sides of the screw slot, and even the toughest screw can be easily tightened or dislodged. It's obvious when the blade is too big–it simply won't fit into the slot. When things go wrong is when the blade is too small. This is where Wagner's explanation opened our eyes to how a screwdriver tip works in a screw. "If the tip is too small, then its sides won't fully rest against the sides of the screw slot," he said. "When only the very corners of the screwdriver tip actually touch the slot walls, the actual force transferred from the screwdriver blade to the screw itself is almost nil."

The more contact there is between the sides of the screwdriver and the sides of the screw slot, the more force will be transferred from the tool to the screw. Also, if you have to push on the screwdriver handle–as well as turn–there is a good possibility that the screwdriver blade is not properly fitted to the screw. Again, the force needed is in the turn–not the push. That's why keeping a screwdriver tip in pristine condition is important. Since proper fit means more power transmitted from the screwdriver to the screw, touching up a screwdriver tip to exactly fit the job is prudent. Although this is a task that can be performed with a hand file, it is easier to use a bench grinder. They are available at most high schools.

Modifying a screwdriver tip to correct damage or to get the blade to exactly fit a particular screw is easy, but there are a few things you should know. The screwdriver has three basic parts–the handle, shaft and tip or blade.

• When filing or grinding the very end of the tip, be sure the resultant surface is shaped to be reasonably perpendicular to the screwdriver shaft.
• When viewing the very end of the tip, be sure that it is as close to a perfect rectangle as is possible. A trapezoid shape is a bad thing. The two large faces of the blade must be parallel to one another, and the two edges of the blade also must be parallel. Each of these sets of surfaces should be square to the other.
• The four tapered sides of the blade are not designed to be shaped to any specific angle. Their pitch can be increased or decreased as necessary to achieve the tip width and thickness needed to fit the screw. Also, the actual length of the blade is not important. Again, the key is to get the blade to exactly fit the slot in the screw head.

Besides forming a tip to be square and be the proper size, the grinding technique is important. Using a grinder is faster and easier than hand-filing, but can cause problems. Higher-quality screwdriver tips are tempered for hardness, and that temper can be lost during the sharpening process if care isn't taken. Temper is what gives a tool its hardness. If the temper is lost, the metal becomes soft. In many cases this can render a tool useless. Grinding can overheat the metal and ruin the temper. The solution is to grind only for a few seconds at a time and then dip the tip in light machine oil. Water can be used, but oil is better. Oil cools slower than water; when you temper, you don't want to cool the metal too quickly. If the tip gets so hot that it discolors (dark blue), the temper probably is lost. Go slowly, and you won't have a problem.