Applying position numbers 

All components of the assembly unit are numbered according to the item numbers recorded in the specification. Item numbers are applied on the shelves of leader lines extending from the image of the component part of the product. One end of the leader line should be on the image of the component part of the product and end with a dot, and the other end should be connected to the horizontal shelf. Near blackened or narrow planes, the dot is replaced by an arrow.

Leader lines should not intersect the images of other component parts of the product, intersect with each other and intersect (if possible) dimensional and extension lines, and be parallel to the hatching lines. It is allowed to perform a common leader line for a group of parts with a clearly defined relationship, placing the item numbers vertically. In this case, the item number of the part in the image of which the leader line begins with a dot or arrow is applied on the upper shelf (Figure 6.3.1.).

The shelves are placed parallel to the main inscription outside the image contour and are grouped into columns and rows. Leader lines and shelves are drawn with solid thin lines. Position numbers are written in a font size 1.5-2 times larger than the font size adopted for dimensional numbers. Position numbers are applied on those images where the corresponding parts are projected as visible and, as a rule, once. It is allowed in some justified cases to re-apply position numbers of identical component parts. In this case, they are distinguished by a double shelf.

Figure 6.3.1

Figure 6.3.2

In addition to reference drawings, the SK may have working dimensions and other parameters (for example, surface roughness, coating) that are used and controlled during the assembly and acceptance of the finished product. These include lubrication holes (Figure 6.3.2), as well as holes for cylindrical and conical pins (Figure 9.), which are drilled during assembly. Such holes are not depicted on the working drawings of parts. For example, the sleeve (Figure 6.3.2) is supplied for assembly without a lubrication hole, and the pipe in the trunnion (Figure 6.3.3) is supplied without a hole for pins.

If the SK drawing has only reference dimensions, then above the main inscription they write: Dimensions for reference, and if there are also working dimensions, all reference dimensions are marked with a sign (*). The corresponding inscription begins with this same sign.

Figure 6.3.3