user8219: For overcoming torque issues, I have attached 2 identical servos on a certain part of my robot arm and because I saw someone do the same.
Now, while writing code I realize:
#include <Servo.h>
...
...
shoulder1.write(map(analogRead(p1), 0, 1023, 0, 179));
shoulder2.write(map(analogRead(p1), 0, 1023, 0, 179));
...

will turn shoulder1 by 20* and then shoulder2 by another 20*, ie. an overall turn of 40*; that too with too much load on servos, as the other servo would be inactive at the time first is active.
I want to achieve 20* fully-sync.ed turn on both servos, how do I accomplish this? Any arduino libraries or walkthrough?

Can I possibly move them both at the same time - something like multithreading on arduino? Here's what I tried:
void rotateTwoServoInSync(int angle) {
    for(int i = 0; i<angle; i++) {
        shoulder1.attach(9);
        shoulder1.write(i);
        shoulder1.detach();
        shoulder2.attach(10);
        shoulder2.write(i);
        shoulder2.detach();
    }
}

Will it work? Is this approach recommendable?

user6834: Spehro's answer is the most obvious. But note that there is no such thing as identical servos. You may stress them if you connect them through a stiff connection.  
If you want to have two mechanical parts make the same movement the proper solution is to connect them mechanically, rather than have two servos doing the same action.

user5080: If you have two RC servos that are always required to move together you can simply connect both control inputs to a single output. 

8219: <p>For overcoming torque issues, I have attached 2 <em>identical</em> servos on a certain part of my robot arm <sub>and because I saw someone do the same.</sub></p>

<p>Now, while writing code I realize:</p>

<pre><code>#include &lt;Servo.h&gt;
...
...
shoulder1.write(map(analogRead(p1), 0, 1023, 0, 179));
shoulder2.write(map(analogRead(p1), 0, 1023, 0, 179));
...
</code></pre>

<p>will turn <code>shoulder1</code> by 20* and then <code>shoulder2</code> by another 20*, ie. an overall turn of 40*; that too with too much load on servos, as the other servo would be inactive at the time first is active.</p>

<p>I want to achieve 20* fully-sync.ed turn on both servos, how do I accomplish this? Any arduino libraries or walkthrough?</p>

<hr>

<p>Can I possibly move them <a href="http://playground.arduino.cc/ComponentLib/servo" rel="nofollow">both at the same time</a> - something like <a href="http://forum.arduino.cc/index.php?topic=4854.0" rel="nofollow">multithreading</a> on arduino? Here's what I tried:</p>

<pre><code>void rotateTwoServoInSync(int angle) {
    for(int i = 0; i&lt;angle; i++) {
        shoulder1.attach(9);
        shoulder1.write(i);
        shoulder1.detach();
        shoulder2.attach(10);
        shoulder2.write(i);
        shoulder2.detach();
    }
}
</code></pre>

<p>Will it work? Is this approach recommendable?</p>
 6834: <p>Spehro's answer is the most obvious. But note that there is no such thing as identical servos. You may stress them if you connect them through a stiff connection.  </p>

<p>If you want to have two mechanical parts make the same movement the proper solution is to connect them mechanically, rather than have two servos doing the same action.</p>
 5080: <p>If you have two RC servos that are always required to move together you can simply connect both control inputs to a single output. </p>
