What is this, slightly ominous, tool used for?

One of the more unusual looking tools in the watch repair industry, these are used to remove and attach glass, They are commonly referred to as a ‘crystal lift’ and a ‘crystal base’. They are very specific tools used to remove something called a Plexi glass. Mostly used in older watches, Plexi glass is a plastic type glass which is easy to polish and flexible enough to resist bumps and knocks. Although it was more commonly used on older watches, some watches today still take advantage of this type of glass.

Most Plexi glasses are a domed shape. The bottom rim has a lip which is used to hold the glass in the front of the watch case and can sometimes be assisted by a metal-retaining ring to help make it a tight fit. The job of the crystal lift is to apply even pressure around the bottom edge of the glass to unhook the lip from the case so the glass can be removed from its case. The crystal base is used when reapplying the glass. The glass is placed rim down into the crystal base – the metal plate on the crystal base can slide back and forth to create the correct sized gap. The metal plate creates a small space for the crystal lift ensuring that the grip around the glass base has just the right gap for the glass lip so that when the glass is applied to the case, the lipped rim can catch the case correctly.