A choke point is an area on the lightsaber hilt where the diameter narrows, allowing the wielder to spin and maneuver the saber more easily. Choke points are a common and popular lightsaber hilt feature, but they are are not used on all lightsaber hilts.
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One common location for a choke point is at the top of the hilt near the emitter. Another common location for a choke point in near the center of the hilt. Some saber hilts, especially longer ones, may include multiple choke points. An Ultrasabers Dominix LE V4, for example, features one choke point up near the emitter and another choke point just below the AV switch.
The saber will spin and maneuver differently depending on the location of the choke point on the hilt and the length and weight of the lightsaber as a whole (factoring in both the hilt and blade). Functionally, a choke point allows for easier lightsaber spinning. Aesthetically, a choke point may also increase the attractiveness of the hilt design.
A little known fact: a ‘choke point’ is also the exact spot on Admiral Motti’s collar where Darth Vader Force-choked him (just kidding!).