I got them from homebase for £2.50, i can't remember what size but i brought my scooter in there and tried out different sizes. It wasnt hard to bolt them - i will put a pic of which bit you put the bolt through if you want.
I Got It Because I Thought It Would Grip It Better But If You Get A District Clamp (The One I Have) And Swiss Bars It Doesnt Fit. ( I Put Card Under The Clamp!)