Complex sentence: Pakistan is believed to have around 40-60 HEU based nuclear weapons.Though Plutonium based research is also available but the estimated stockpile is not enough to be comparable to Uranium ones, however the specifications of these are not available publicly.
Split into simpler sentences: Pakistan is believed to have around 40-60 HEU based nuclear weapons. While Plutonium based research is also available, the estimated stockpile is not enough to be comparable to Uranium ones, and the specifications of these are not available publicly.