Hitec servo high torque travels 180º - full-lock to full-lock - to hold your gear in position securely. Not proportional. Perfect for mechanical retract installation. Water resistant Ball bearings. A retract servo is a very specialized servo. It is non-proportional, going 180 degrees, lock to lock. They are specifically made for mechanical retracts to lock the gear in the up and down positions. they DO NOT have any means of end point adjustment and can not be adjusted by ATV on a transmitter. They are only able to go 180 degrees and provide full maximum available torque at the two end points. This is their whole purpose and intentional design, but if someone has a unique design situation where they need other than 180 degrees available, then they must use a proportional servo, not a retract servo. They are specifically designed to wit'stand constant holding loads in the up and down positions, unique to the use of mechanical retracts. Pneumatic retracts do not need a retract servo. A proportional standard or mini servo is used to move the air valve back and forth.