The GWS Micro Servo has metal gears to deal with significant torque, but is built into an a very small, compact package. Comes with several different servo arms as well as mounting hardware.

GWS Micro Servo SPECS:

Length: 1.17"
Width: .55
Height: 1.10"
Weight: .63 ounces
Torque: 25 oz/in at 4.8V / 32 oz/in at 6.0V
Speed: .16 sec/60 degrees
JR-style universal plug