The invention is directed to a hand-wheel for adjusting an outlet pressure and/or a flow-rate of a tap for a gas cylinder, the hand-wheel comprising a body; and a transparent cover fixed on the body. The hand-wheel further comprises indicia arranged between the transparent cover and the body so as to be visible by a user but not in contact with the fingers of the user. The invention is also directed to a tap for gas cylinder, comprising such a hand-wheel, as well as to a tap assembly comprising such a tap and a cover housing the tap.