This is a HS-5745MG Digital Quarter Scale Servo with S Plug.

FEATURES: Triple ball bearings
Water and dust tight
Durable heavy-duty metal gears with one resin gear
Comes with "S" servo plug installed
Programmable digital amplifier
MOS FET amplifier
Super efficient heatsink
Heat treated metal servo arm
Gold plated contacts

INCLUDES: One servo
Black round servo horn
Black long double straight servo horn
Black long and short single straight servo horn
Blue anodized heat treated long double straight servo horn
Four servo grommets
Four brass eyelets
Four S/T servo mounting screws

SPECS: Length: 2.32" (59mm)
Width: 1.14" (29mm)
Height: 2.04" (52mm)
Weight 5.68oz (161g)
Operating speed: .18 sec/60 degree at 4.8V
Output torque: 208.30oz. in (15Kg.cm) at 4.8V