I got these rings for a Sako S491 222. These one piece ringmounts in low are actually lower than the low 2 piece base and ring optilocks, which I found too high for a scope with a 42mm objective. They are also lighter and less bulky looking that the 2 piece optilocks, which I like on the small actioned 222 Sako. The rear has a stud that mates up with a corresponding pocket in the receiver, the forward ring is very adjustable, lots of room to move it fore and aft for optimum scope positioning, good for getting correct eye relief with shorter scopes. They are expensive, but well worth it given the fit, quality and adjustability. You also get great protection for your scope tube with the synthetic ring inserts.
I’ll probably buy another set for my M591.

Excellent Ring mounts, great service.👍