I had one of those on my GZ. Its a good buy for the money. 7/8" is what you want. Clamps on and off very easy. Problem is finding that sweet spot where its doing its job and also in a good looking spot and not too high. For chest off deflection it does great mounted with the bottom rubber of the shield resting on the headlight (also keeps it mounted very sturdy). but for me being 5'9" i got very bad head bobble from the wind whipping over the top. Ended up having to raise it very high to defeat the bobble
see example. Worked great, but sat too high and looked kinda weird. If they would sell those in 19" high .. those would be perfect. My head bobble also was while wearing a half helmet, never did try it with the full face, might not have been so bad with that on. They arent super thick, but they dont wobble at high speeds either.
Oh yea, one thing with those...when playing around with the height, dont clamp it down hard or you'll end up with screw marks in the flat black paint of the bars. I adjusted mine up and down so much that the bars looked like i beat them on the edge of a drum. The paint comes off very easy leaving you with aluminum marks all over the place. Once you got the spot where you like it, THEN clamp them down good. Otherwise you'll be taking them off and repainting the flat black.