Investors seeking damages in the proposed class action said banks did this to preserve their 70 percent market share, and boost profit by making trading more costly. Engelmayer dismissed all claims against the 12th bank, HSBC Holdings Plc. Interest rate swaps let parties exchange future interest payments, typically by exchanging a fixed rate for a floating rate, to manage risk or bet on whether rates will rise or fall. Banks have faced many private lawsuits and regulatory probes into alleged rigging of derivatives, rates, securities and commodities. In his 108-page decision, Engelmayer said the complaint by investors led by the Public School Teachers' Pension and Retirement Fund of Chicago and including the city of Baltimore was "rife with specifics" about alleged collusion in swaps.