Bowen's website says Ruger Double Action. It doesn't specify model, just that older Redhawks have a pinned bushing and newer ones don't.
They also sell a tool for the screw in type. I'll know more about it in a couple of weeks after I order one for the Super GP and my Redhawk.
Meanwhile:
http://parts.bowenclassicarms.com/index.php?main_page=product_info&cPath=8&products_id=49