A thickness gauge, sometimes referred to as a degree gauge uses the simple device of having a much longer arm on the reading side to magnify any movement from the measuring side of the pivot. Thus a small gap between the tips becomes a much larger swing of the measuring arm and a reading can be taken from a suitably calibrated scale fixed to the opposite leg.
This model will measure between 0 and 15mm in increments of 0.1mm and has a throat depth of 20mm. Taking the sharpness of the pointer into account and the effects of parallax you have a great value tool that will give you a reading with far more resolution than anything else in this price range. All steel construction, overall length 155mm.
Our cycling staff have found this an excellent tool for measuring cycle rims for wear.