here is the line from the rubi page
the jewels, are the red (usually ruby, or synthetic rubies) jewels you see below, in the watch movement. the blue, are the heads of blued steel screws. the jewels are placed at points in the movement, where there are gears that would create significant friction. and using a hard jewel, prevents the friction from damaging the movement. see below. also, i think that reads 52 jewels, on this lange. that is far above the norm.