[RichardJ]

I have a box of match books. .017" for the cover and just under .015" for the match sticks. .019" is for NEW polished contact points. Used points, even when filed relatively smooth, have to be set with a thinner gauge to achieve the desired dwell.
Match cover thicknesses do vary, but more accurate than eyeballing it. In the image, a 016" gauge can produce a really wide gap if you don't do some cleaning.

I have done it myself. With a screwdriver, a matchbook found on the side if the road and a street light to see by.