This is, in my experience, the only tool one needs to open a threaded watch caseback, which are found mostly on ‘waterproof’ or water-resistant wristwatches. It’s definitely a two-handed operation, but can be done by hand, with no other tools. The wrench comes with several sets of different-shaped pins, which you arrange on the tool to match the precise notch pattern on the caseback. This wrench will work with casebacks that have notches in amounts divisible by 3 and divisible by 2, which makes the tool adjustable to just about any size caseback.
It’s not apparent from the appearance, but the tool’s large handle rotates to adjust the bottom pin, and the thumbwheel in the middle adjusts the two pins above. Takes a little getting used to, but it’s a good, solid feel when the adjustments are correct. Slow, constant force works best; no need to quickly jerk anything.
This type of tool is available from other stores, but Harbor Freight offers the best value. I’d say mine paid for itself about fifteen times over during the first week I had it. Over the last few years I’ve had several batteries run down on watches I own, including a Fossil titanium watch and a no-name Army field watch. So far, I have only used the tool’s round, pin-end pegs. I’m actually not sure what watches require the other types of pegs included, but it’s nice to be prepared.
Be aware the possibility of marring the caseback exists, and therefore you should be moderately careful when using this tool. Marring hasn’t been an issue with the watches I’ve fixed, but if the metal is soft (gold alloys, for example), or if you’re not careful, this could easily happen. The pins on the wrench appear to be hardened steel and would very likely be much harder than the watch caseback.