The watch spring bar tool has three basic elements, and I've used all three.  On one end, it has a claw, like the nail-puller on a claw hammer.  On the other end, it has a drift-pin.  And in the middle, it has a metric and an imperial scale.  The middle section has a hexagonal cross section which seems trivial , until you've had cylindrical tools roll off your work area a few times.

The 'nail-puller' is for easing spring bars out of their sockets on watches when you are changing bracelets or straps.  The drift pin is for resizing watch bracelets.  The scale is for checking the size of strap or bracelet, but, of course, can be handy for any small linear measurement.  The drift pin is not the ideal tool for removing a link from a bracelet, but works passably well with practice.  Generally, one of the little widgets that looks like a miniature press or vice is a much better tool, but this one takes less space.

It's been a very good little tool, and I've gotten a lot of use out of it.  No watch aficionado should be without it.

E. M. Van Court