USE Tula Aero Bar Extensions - Carbon Ski Bend From  £67.49

Bought the 50 degree bars to adjust my TT position. The diameter of the bars are a standard size. They fitted fine on my bike (S-works Shiv TT).

These bars are very nicely made. They come with a plug to put in the shifter end if you don't have a shifter and also a plug that goes inside the clamped end to prevent the bar from being crushed when clamped.

The inside diameter of the clamped end is smaller than the shifter end so it would be difficult to use them back to front, if you wanted to do that.