A scriber-block is an instrument consisting of two principal parts ; these are the movable scriber, and the block to which the scriber is attached; the other smaller pieces are the fastenings by which the scriber is fixed to its block after the scriber-point is raised or lowered to any particular height which is necessary. That portion of the tool termed the block, is a small pedestal, which may be of wood, steel, or any other metal, the principal requirement being lightness combined with stability. Scriber-blocks are principally used to mark straight lines upon engine-work of all classes, large and small, and all scriber-blocks are used on plane surfaces, named surface-plates. The process of scribing consists in laying the piece of work upon the surface-plate, or upon a few packing-blocks that may be on the plate, and moving along the scriber-block with one hand or two hands while the soriber-point is in close contact with the piece of work to be marked, and the base of the block touches the surface-plate; consequently, all Unes made with a scriber-block thus used, are straight, and also parallel to the plane on which the block is moved. If a scribing instrument of this character is properly made, and the surface on which the block is moved, is clean, all lines made with the scriber-point as much resemble straight lines as that portion of the surface on which the block moves resembles a plane. Scriber-blocks will mark any number of straight lines upon a piece of work, or upon several pieces of work, so that the lines may be of the same or of different lengths, also at various angles to each other, and at the same time parallel with the plane; also, several lines may be marked upon one piece of work so that all the lines shall be parallel to each other ; and this is effected by raising, or lowering, and fixing the scriber-point to the various heights that the lines are required to be above the surface-plate. This property of marking parallel lines is the most important quality of the instrument, and renders it applicable to the scribing of work of all sizes and conditions ; scriber-blocks are therefore made of various heights, from one inch to several feet, and the height of the particular block selected for use depends on the distance to which the piece of work extends above the table or surface-plate.

Scriber-blocks are represented by Figs. 277, 278, and 279. By referring to these Figures, it may be observed that each scriber is bent at one end; this bent part being used for making lines upon the top of a piece of work, and the straight end being for the lines that are required on those surfaces of the work which are at right angles to the plane on which the block moves. The block shown by Fig. 277 is of wood, and the two other blocks are of iron or other metal. Fig. 279 denotes a tall block which becomes an el-square by taking off the scriber.