Kreighoff makes the quality ones for all guages. They are fully adjustable for windage and elevation and retain their zero when removed and reinstalled. They are intended for use in combination guns and drillings which of course have sights and/or scopes. Mine ( 20 gauge) will stay on a dime all day at 20 yards with Winchester Super X, minute of grouse head. After initial zeroing it removes and installs in seconds. About a foot long, it costs about $40 per inch.