It says the clamp is 1.5" inner diameter on the Saberkit site, so easy enough to confirm if it's too small for the saber or not. I'm guessing Lord Bane is right, though...
And I thought Hasbro had only done the Vader ANH?
As GreyJedi queried, the ANH has the clamp 'lever' and ESB doesn't - and the ESB has the wires and the ANH doesn't.
The ANH has shorter t-grips not all the way up to the clamp, but the ESB grips go right up to the clamp.
It sounds like yours might be the Vader ANH rather than ESB from the description you've given.