A watch needs a screw to attach its parts together especially to the mainplate. They are very useful to put things in place. They secure the parts of the watch. They are ideal in watch making because they sturdily secure the parts at the same time can be removed conveniently.
Before screws were invented, tapered pins were used in watch making. Watches are invented before the screws were. Using tapered pins is very challenging because they are difficult to remove. Removing them can scratch the movement thus can easily affect its overall quality. Screws are a lot better than tapered pins because they can easily be removed. They are made of steel securing a strong force. Up to date, there is no other alternative to screws because they are the most practical to use in watch making.