1PN51 (Russian: 1ПН51) is the GRAU index for a Soviet designed passive night scope for a range of Soviet designed small arms and grenade launchers. 1PN is the GRAU index of night vision devices, where PN stands for Nochnoy Pritsel (Russian: Ночной прицел) meaning night sight. The scope weighs 2.1 kg and measures 276 mm × 210 mm × 140 mm (length × height × width). It is attached onto a matching side rail on the weapon after which a lever on the scope is pressed to hold it in place.