Was wondering about watchmaker screwdrivers…

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Why do they have two threaded holes by the tip, but only one is filled with a screw?
 
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The blade ends have a flat edge on one side to keep them from turning.

Probably cheaper/easier to manufacture with a straight through hole.
 
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The blade ends have a flat edge on one side to keep them from turning.

Probably cheaper/easier to manufacture with a straight through hole.

On mine, both holes are threaded, so I’m still puzzled as to why the make would bother threading both if they didn’t need to. I can only it’s a spare in case one side gets buggered up.
 
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It's simply a manufacturing expediency/efficiency.
To only have one side drilled and tapped would require precise drill depthing and two threading taps (one start/one bottoming).
A straight through hole only requires a single pass with a drill and a single tap to do the threading.
 
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It's simply a manufacturing expediency/efficiency.
To only have one side drilled and tapped would require precise drill depthing and two threading taps (one start/one bottoming).
A straight through hole only requires a single pass with a drill and a single tap to do the threading.

Thanks Jim, appreciated.

I don’t have a tremendous array of screwdrivers, but I notice when I pull a blade out for replacement, on the bottom, there’s a rounded end, and on the other side, a flat spot, where I’m assuming the screw is supposed to abut up against.

But on my screwdrivers, when you stick any blade in, they spin freely, meaning the flat spot does not automatically line up right under where the screw is supposed to go. So you have to do it by feel. Is that how most of them are constructed, even the better quality models?
 
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Thanks Jim, appreciated.

I don’t have a tremendous array of screwdrivers, but I notice when I pull a blade out for replacement, on the bottom, there’s a rounded end, and on the other side, a flat spot, where I’m assuming the screw is supposed to abut up against.

But on my screwdrivers, when you stick any blade in, they spin freely, meaning the flat spot does not automatically line up right under where the screw is supposed to go. So you have to do it by feel. Is that how most of them are constructed, even the better quality models?
Just tested, this is indeed the case on my bergeon set, the flat of the screwdriver itself though lines up with the machined flat for securing the bits though, so I guess you could use that to line it up?
 
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Is that how most of them are constructed, even the better quality models?

Yes. Just so you know, none of the other screws we install every day are guided in place either. 😉