Common Parts : LT-Tool-LT-0002
If your Helicopter does not fly very stable or vibrating a lot, or you see a "Double Blade" effect on the main rotor, there could be many reasons. One of the big reason is the weight of the two main blades are not the same.

This balancer is designed for balancing the main blade with 3mm hole (Usually 400-450 Class Helicopter)

Main Blades are made by human hand, sometimes they may have very slight weight difference, when they were put on the rotor, the spinning will magnify the weight difference and causing the helicopter to vibrate. That's why the weight of all main blades should be fine tuned carefully.