den-den,<P>I don't know for the Ruger P90, but it should be the same for all tapered dovetails. Measure the width of the dovetail on both sides and drive towards the big end. You'll probably need a pair of calipers to measure it accurately, unless you have a machinists rule with fine gradations. Some sights are staked, so you might need a really hard dowel or a brass drift punch to knock it out.
