Why not just make it one shape, in different sizes?
In: Engineering
Let’s say an industrial buys their initial screws and tools from company A instead of B because at the time it is more advantageous. Later on, the industrial needs more screws and at this point B seems more advantageous. Thing is, you bought your tools from A and they are not compatible with the screws from B so you are highly encouraged to pursue business with company A. Company A ensured that you would keep doing business with them by making their products non compatible with other companies.
Another reason is the reluctance that industrial have towards letting their customers repair their own products. They would rather have you buy a brand new one. If you don’t have the proper tools you might quickly get discouraged from trying to open, investigate and repair your broken possessions, you are more inclined to dispose of it and purchase a new one or to send it to the manufacturer for them to repair it.
I am sure there are other reasons, the thing is to put yourself in the shoes of those that benefit from this.
Different shapes are good for different applications. For example, flat head or slotted screws are easier to manufacture; many screws in handmade watches tend to be slotted for this reason. Allen head screws can accept a good deal more torque than a slotted screw, and the driver is less likely to climb out of the fastener. The robertson screw head was designed to make it easier to manufacture screws by cold forming, and are easier to screw in one-handed than slotted types. Some types, often called collectively “security” or “anti-tamper” screw, are specifically designed to not be common, so that no one can use common tools to open them.
That’s how it was for a few hundred years, there were a slotted screws and that was pretty much it. I have seen tanks with armor plate held on with slot-head screws the size of Eisenhower Dollars.
Problem with that is that slot-head screws are very prone to cam-out where the screwdriver slips. Phillips was designed to cam-out on purpose as a torque limiting design for factory assembly with power tools. At the time there were no torque limiting clutches on power screwdrivers. Robertson drive (square hole) is designed to be unable to cam-out. Star Torx is designed for high torque applications but is badly misused by the industry as a “security fastener” and in applications where it has no benefit. The little vanes in a Torx fastener are very suceptible to rust and a rusty one will disintegrate the instant you apply the tool.
There are a multitude of foolish “security fasteners” that get used in places where someone thinks that their use will keep someone out of a device, but the fact is that physical access to the system is total access to the system. The appropriate tool will be acquired or manufactured, or the fastener will fall to the hammer and chisel or the cutoff wheel or the drill. All these do is frustrate repairmen who want to be able to put it back together neatly, someone tearing into it to seek vulnerabilities or acquire intellectual property will not be meaningfully delayed by such fasteners. The other time you find them is when someone is trying to hide poor construction. Whenever I see them on something that otherwise has no reason to (no trade secrets or security functions or intellectual property or suchlike) I open the device up to see what is being hidden.
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