PK23 or PK02 is an older but interesting red dot design. By itself it doesn't have a built in mount and is intended to be paired with the side rail or top cover mount of your choice. The tube is 30mm and should fit most aftermarket rings and mounts.
The interesting part of the PK23 is that is has a flickering red dot of approximately 1.5moa. While small the flickering aspect naturally draws your eye to the dot and makes it easy to acquire in a hurry. While not as common as they used to be the PK23 has a very good reputation from it's owners and is well liked.
Show here in the RS Regulate 30mm Aimpoint mount. PK23 will cowitness in this mount if the rear sight leaf is set on 3 or 4, or battlesight (which is 4 for the SGL31/AK74)
Quick photoshop of what the reticule looks like when cowitnessed