NSE has revised lot sizes for four indices, effective October 28. The Nifty 50 lot size will drop from 75 to 65, Nifty Bank from 35 to 30, Nifty Financial Services from 65 to 60 and Nifty Mid Select from 140 to 120. Lot sizes are the minimum shares that can be traded in one futures or options (F&O) contract.