Popular in both construction and electrical fields, the Robertson drive (commonly referred to as the square drive) is more common in Canada than the US due to licensing problems earlier in its history. This makes it easy to determine the key needed for a specific hex screw when you’re not sure of the size. To measure an unmarked key, for example, you would measure the distance between two opposing ends. Measurements for hex keys is done via AF (short for across flats). More commonly referred to as Allen wrenches, these screwdrivers sometimes come in an L-shaped shank with no handle, as multiple retractable sizes with a centrah handle (ala Swiss army knives), or even with a ball-shaped tip. Hex keys are named because they have a smooth hexagonal shank and no head. Pozidriv bits have a “PZ” marked on them along with five common sizes. A Pozidriv bit will not fit inside a Phillips fastener. While you can fit a Phillips bit in a Pozidriv fastener, it will likely cam-out before you can fully tighten it. This allows for increased grip between the bit and fastener. Instead of the Phillips’ pointed tip, tapered flanks, and rounded corners, a Pozidriv has a blunt tip, parallel flanks, and an additional small rib between each slot. This screw drive is often referred to as an improved version of the Phillips drive. Note that the length of the handle is proportionate to the length of the shank, so short-shanked drives also have short handles. The shank length will affect whether the screwdriver can fit into a deeper recess (perfect for automotive work) or if it functions best where there’s very little room for your hand. These measurements are presented as width by length (for example, 1/8″ x 4″). The good news is that the width of the tip and the length of the shank are presented in the measurements provided. Unfortunately, the way flat head screwdrivers are measured can be frustrating, as the thickness of the tip is rarely given. You can often use a slotted screwdriver to work heads with a slightly bigger slot or even Phillips (or other cruciform style) heads in a pinch. Commonly referred to as a slotted screwdriver, these have the wedge-shaped blade that any child immediately recognizes.
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