For the dulcimer I use the red ones, the thickness is actually not documented anywhere.
Jergen, if you mean that the thickness is not given in millimeters, you are correct. Here is the website describing the three gauges of the picks: thin, medium, and thick. Herdim Picks
I'm not sure, but I think the points have more to do with stiffness, rather than thickness, with I being the least stiff and III being the stiffest. As I noted below, people have measured the thickness of the pick and points, but the measurements vary widely.
"The dulcimer sings a sweet song."