A web and sheet sluice adjustable to different material thicknesses for sheets of paper or the like, which are fed to a processing or treating unit. The sluice has a passage gap between a friction roller, which rotates continuously during the working operation, and an axially parallel braking roller, which is radially adjustable in relation to the friction roller. An electric switching element sends a control signal for an electric circuit during the adjustment of the passage gap to the thickness of a sample located in the passage gap. The braking roller is rotatably mounted on the cylindrical eccentric of an eccentric shaft, which can be driven by a first electric motor drive and can optionally be adjusted to both directions of rotation, and with the friction roller stationarily stopped, it can be driven by a second electric motor drive at a speed of rotation that is substantially higher than the velocity of adjustment of the braking roller via a driving gear which can be moved out of its normal position. When the gap width to be set has been reached, the switching element, by the switching signal of which the two electric motor drives are stopped, is actuated.