I found a used internal throttle on ebay saying this:

"Designed for 1 inch handlebars. The outer diameter of the portion which locates into the handlebar is 0.82" the diameter of the portion covered by the grip is 1.15". "

but I dont know if it will fit my bars

 

I do not have an exact figure because I've seen different sizes on different bikes. But the two most prevalent sizes for 1 inch OD tubing are 0.065" wall thickness/0.870" ID, and 0.082" wall thickness/0.834" ID. That said, I have several stock and aftermarket sets of bars that have the 0.082 wall and the various internal throttles I use are all a semi-sloppy-to-sloppy fit. Depending upon how the throttle fastens to the bar it can be shimmed if needed.

 

Just measured the 'Bones bars I have on the shelf at 0.870" i.d. and 0.065" wall thickness.