For some reason, the number 6 was never assigned to any Rivethead issue.  We think this to have been a simple oversight, as Issue #5 came out in April of 1989 and Issue #7 came out the following month in May.  It could perhaps be something more sisister, for without 6 there can be no 666, but we think that's stretching it a bit.  Okay then.  On to Issue #7 with you!