For one, it's the wrong caliber for an AK!
Headspace is the distance from the bolt face to the chamber face (end of the barrel). When the weapon is fired, the pressure forces the barrel out and up against the barrel pin. If the barrel is not forced up against the pin, when it's fired, the headspace will change and cause a very bad situation.
Midway (and many other places) sell "go/no go" gauges to make sure the headspace is good.
Yeah, the look the same to me as well; but If the action closes with the first gage inserted, then the firearm is within acceptable minimum headspace dimensions. If the action closes with the second gage inserted, then the firearm may not be within acceptable maximum headspace dimensions and should be examined further by a knowledgeable gunsmith.
Most builders use both to make sure it's good-to-go!