there's not a particular score or cutoff which I can tell you, you can qualify mains by scoring even 20-25 marks but that will not assure you a seat in NITs or IITs you have to work hard for it, if you want to get admission in top NITs or IITs try to score more than 150 marks as with PWD certificate these marks will be more than enough to get you into any top NIT or IIT.

hope it helps.