All bolts must have a number, which is stored in the NUMB attribute of the Bolt Point. Bolts must be numbered in order around the bolt circle, except for jacking bolts, which will have NUMB set to zero. Thus bolt number one on a flange will correspond to bolt number one on the connecting valve, and so on (see Figure 4:4.: Example Data Flow Diagram for a Wafer Lug Valve). The bolt order must be symmetrical, so that two like flanges can be bolted together when one is reversed.