The Ruger Security-Six, Police Service-Six and Speed-Six double-action revolvers, introduced in 1970 ... allowing for single-action fire, or that were smooth and allowed only double-action fire.
it’s also been bestowed on a rimfire single-action (SA) revolver made by one of America’s Big Three handgun manufacturers. Say hello to the Ruger Wrangler .22 Long Rifle (.22 LR) revolver.