Two types of projector are described which permit the continuous observation of the sectional shape of a rod-like or thread-like object, of substantially constant cross-sectional shape, as the object is passed through the projector. The article may be of any length and may be flexible or rigid. The projection of sectional shape may be accomplished by two distinct methods. The first employs the projection of light scattered from the surface of an illuminated peripheral band of the object. In the second method the object is placed co-axial with a projection lens which receives scattered light from all points on the surface of the object under examination. The lens selects a thin section of the object and projects the peripheral shape of this section on to a screen. The application of these projectors to the continuous gauging of the outside dimensions of rubber tubing is described.