I’ve installed several sets of On Target sights I got from Scarlett.
The inside top thickness of the slip on sights is about.040”.
I remove that amount from the top of the revolver sight. Then I measure the barrel to top of sight. I remove material from the bottom of the brass sight to achieve the above measurement. Clean everything with acetone and use red loctite. Tap the brass sight down flush with the barrel and the height is the same as the original.