Indian equity benchmarks BSE Sensex and NSE Nifty50 are likely to make a gap-down start on Thursday tracking weak global cues after the Fed announced a 75-basis-point hike in benchmark interest rates as widely expected.On Thursday, Singapore Exchange (SGX) Nifty futures — an early indicator of the Nifty index — fell as much as 181.5 points or one percent to 17,981 ahead of the opening bell on Dalal Street.