There are several bars on the market which are adjustable for various diameters by means of micrometer screws and taper wedges. These are useful for many purposes but space will not permit a detailed description nor has it been the writer's purpose to deal with the many varieties but rather with representative types. Special bars for many purposes, porcupine bars and cutter heads of various kinds, have not been described, because these are not single-point boring tools. Neither has mention been made of boring tools such as are used in fixture work on the horizontal boring machine, for these are found in every tool-room, in all shapes and sizes.

In several of the illustrations it may be noted that the tools are shown in a plane parallel with the rotation of the turret. This has been done simply because the details are more clearly apparent when shown in this way. Greater accuracy is obtained by setting the tools in a plane perpendicular to the turret rotation, as previously stated.