Ruger introduced the XR3 Red (Redesigned) grip frame in 1962 to replace the original XR3 frame. These frames are on the 1962 and later Single-Six, Super Single-Six*, Blackhawk, Hawkeye, & Old Army.
These grip frames were modified in 1972/1973 for the new trigger spring and safety transfer bar, but they retained the same basic profile. These frames are on the New Model Single-Six, Super Single-Six, Blackhawk, Super Blackhawk with 4-5/8" & 5-1/2" barrel, the 1993-2005 Vaquero, & the New Vaquero .44 Magnum. (They do not fit the Flattop Blackhawks.) (Early models had "Alcoa" stamped on the frame.
The standard Single Six had a fixed rear sight dovetailed into the frame, and the Super Single Six model came with the same fully adjustable rear sight as a Blackhawk. The Super also came with a ramp front sight