Not the intended purpose, but as-is, or better yet with a bit of augmentation, these make a useful tool for measuring guitar fret height. Helpful when evaluating wear if you have a thing for measurements; a good luthier would likely immediately judge by look or feel, and wouldn't care whether they are 38 thou or 42 in height...
Stupid value for the money, but it's only this cheap for us because labour resources are getting screwed over somewhere far away. Unemployed people at home; slave labour overseas....yay!