Unit 4 Title Blocks and Notes 53 Copyright Goodheart-Willcox Co., Inc. tolerance limits specifi ed for the drawing. Refer to Figure 4-4(R). Tolerances can be specifi ed for one (.X), two (.XX), three (.XXX), and four (.XXXX) place decimal dimensions, or for fractional, metric, and angular dimensions. The limits in the tolerance block apply to their referenced dimensions unless a dimension has a specifi c tolerance noted. Surface texture is the desired surface condition of a manufactured part. Surface texture or surface fi nish tolerances are noted on the part drawing, but can also be included in the tolerance block. Machined parts usually require certain surface textures. A value system with a designated number describes the surface texture. As the value of the number decreases, the surface condition improves. Surface texture numbers vary anywhere from 2000 to .5. See Figure 4-7. Application Block The application block is used to identify a part’s assemblies, systems, and subsystems. Application blocks are typically located at the left side of the title block. Refer to Figure 4-2(6). The NEXT ASSY column identifi es a part’s next higher assembly with a number (drawing or part) that corresponds to its next higher assembly drawing. See Figure 4-8. The USED ON column is used to match a part to its system or subsystem. Revision History Block The revision history block, revision block, or change block is a record of a drawing’s changes. It is becoming less common for prints to include a revision history block on the sheet. The revision history is stored digitally, and only the latest revision letter appears on the sheet. When the revision history block does appear on a print, the block of information is generally located in the upper-right corner of the drawing as shown in Figure 4-2(8). However, it is common to be located in the title block area. Unspecified tolerances may vary from part to part. For example, the tolerance for a two-place (.XX) decimal dimension may be ±.010 inch for one part while another part may use ±.015 inch for two-place decimal limits. In addition, one company may use one set of tolerances while another company’s tolerances may differ. Identifying the tolerances before machining a part will allow you to make the part to the required specifications. PRO TIP Goodheart-Willcox Publisher A tolerance block gives general tolerance limits that apply to dimensions that do not have any specified tolerances. Figure 4-7 Goodheart-Willcox Publisher The application block is used for recording a part’s assemblies and subassemblies. Figure 4-8 The part is a component of this assembly The part is also a component of a main assembly APPLICATION NEXT ASSY USED ON