For those requiring a really heavy duty servo arm, the Dubro Super Strength arms will fit the bill.
Features: Black composite plastic servo arms
Mounting holes at: 12, 15 and 18mm
Total Length: 23mm
Mounting holes at: 15, 19, 22 and 25mm
Total Length: 30mm
Mounting holes at: 23, 25, 28 and 32mm
Total Length: 36mm
Dual Mounting holes at: 15, 19, 23 and 26mm
Total length: 28mm
Note: All measurements are from the center of the arm. The dual is only from one side to center. The actual overall length is 56mm. It fits the FUTABA servos with splined output shafts.