The Rigby type, as Daryl pointed out, were windage adjustable by tapping the sight left or right in its horizontal dovetail.

Lyman made these:

Lyman Model 1A

Lyman Model 36

The Lyman 36 mounts on MS bolt release, swings away as bolt is drawn through split bridge, returns to zero as bolt closes.

Lyman offerings in the 1939 Stoeger catalog

Parker Hale crafted these top shelf items, fully adjustable

Steyr offered these flush mounted numbers as 'cost options' on the Mannlicher Schoenauer

They are a dandy bit of kit - My M1910 Take Down has one. When not in use they fold down with the light push of a thumb.

Special folding peep sight.... $12.00