This is the ASD-M4 rear sight for the Saiga shotguns, as sold by rusmilitary.com. It is new. It is supposed to fit in the existing rear dovetail, for use with one of the AK style front sight attachments for these guns (rusmilitary also lists those). I ordered it from rusmilitary and never used it. Price is $15 including shipping, which is less than what I paid for it, all things considered.