Derivatives Analyst Shilpa Rout recommends that investors be very cautious on Bank Nifty and that it is important to be stock specific in sectors like metal. The range for Nifty on a broader basis is now between 17,000 and 17,250 odd zones. The Bank Nifty has a very weak structure. A very heavy unwinding is happening at immediate strikes and it is ready to break 39,000 and might slide towards 37,000 odd zones.