Love my K-31 and have a St. Marie mount on the way.

What rings? Suggested height for the usual 40mm objective scope?

You will need European rings for the St Marie. I think they are 11mm dovetail. I cannot remember which brand or where I got mine but here are a couple of pictures to give you an idea of the height and how much clearance with a 6x40 scope.

Yes the mark on the scope is from the ejecting brass. Since it is a cheap scope I do not mind it but if you plan to put some nice glass on yours I advise a remove by hand approach to your brass.

I got these, not the 11mm ones though. Don't know about the height you need, since I'm using a Leupold VX2 1-4x20.

tag

I use the Millet .22 steel Angle-Loc Rings. Mid height is good for 40mm. High for 50mm.
Cost about $18 with C&R discount at Brownells.
www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=9078&title=ANGLE-LOC?%20.22%20SCOPE%20RINGS

The Warne 7.3 .22 rings are also hightly recommended but often not in stock and more costly.
www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=16768&title=7.3+RINGS