An on-line interactive network community for the integrated purchase and sale of metals, particularly steel, is disclosed. Other club heads include: a club head body having a ball striking face and defining a rear cavity; and an insert member in the rear cavity, wherein the insert member interior includes one or more chambers facing the rear surface of the ball striking face. Signals generated by induction are intercepted and, using a back-projection algorithm including a suitable weighting factor, are converted into contrast information. The secondary wafers are bonded onto the primary wafer. An outer lead is arranged on a second side surface of the resin package to serve as an external source electrode.