There are many brands of Internal throttles available. Some made abroad will not fit your 1" grips without remachining the grip to make it fit inside. Others will fit but are hard to twist, A company called Streamline Designs offers a "strret legal" internal throttle running smoothly on bearings. The twist needed to reach full throttle is also much shorter than older designs. Result: no more re-griping to reach full throttle. Exactly the way it should be. This company also build a few full blown custom bikes. Streamline Designs.