No, no, not for scribing your pockets...
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Some years back, at a yard sale, I picked up a Starrett No. 70A pocket scriber, which immediately became my tool of choice for scribing layout lines on metal (preferably on Dykem, but it will show lines on oxidized surfaces too). For those not familiar with them, pocket scribers hold what Starrett calls a "point" - a shaft tapered to a very fine point, and tempered hard enough to scribe metal cleanly - in a shaft with a collet and knurled collar. Open, they look like this:
Starrett, as you might guess from the photo above, offered (and still offers) them in two sizes (small 70A and larger 70B). Perhaps the different sizes are more or less prevalent in different metalworking specialties, or perhaps it's just a matter of personal preference. What makes them pocket scribers is that the collar can be loosened and the shaft reversed in the handle, thus allowing you to put them in your apron pocket without stabbing yourself - and without damaging the point:
Even though I don't put the scriber in my pocket, I do "close" it to protect the point before putting it back in the drawer.
You may be saying, OK, but what's the reason for this here post? I acquired the No. 70B scriber pictured as an inadvertent* part of a purchase from That Auction Site of a pair of 6" dividers, and, in fooling around with them on their arrival, I realized that there's a very simple, yet brilliant, engineering element in play here. The shaft for the point is full diameter for part of its length, and then tapers to the point:
The hole in the handle is bored to the full diameter of the shaft for less than the length of full-diameter shaft, then to a smaller diameter for the remainder of its depth, thus offering a shoulder (at the transition from full-diameter to smaller hole) to register the shaft against in open position so that the shaft doesn't slide back into the handle. The placement of the taper in the length of the point ensures that a little bit of shaft sticks out when the scriber is in closed position so you can remove it when it's time to use the tool. And the smaller boring goes all the way to the end of the handle, thus ensuring that the point is suspended in space/doesn't make contact with anything to damage it, when the shaft is in storage position.
It's a "well, duh!" solution - how else could these have been designed? - but it solves several problems at once in the simplest possible way, making for a very useful little tool.
Other manufacturers seem to have thought it was a good idea, too - I also have a Lufkin model, the one with more patina in below's picture
although it came with the point dulled, and I've never gotten around to sharpening it...which brings up another benefit of this design. Chuck the shaft in a drill motor, and you can sharpen the point quickly on a wet wheel or lubricated oilstone/waterstone/wet-n-dry sandpaper so it doesn't burn.
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*That is to say, it's now a extra/redundant tool in the herd.
