Used Tune mtb stem. Amazingly light, strong and beautifully made. I've changed to a shorter stem.
CNC machined from 7075 T6 grain orientated heat-treated Aluminium, with custom-made 'Load Specific' hardware.
It has a tapered design (inside and outside), for ideal load distribution, and a removable front plate for easy bar / stem change.
Machined apertures at the steerer clamp section save weight without affecting strength.
Or - translated from http://www.tune.de:
'This is the best combination of stiffness, weight and safety. Conical shape, inside and outside, according to the force. Light Bars (de) montage by removable front section. Very fit for the clamping of carbon handlebars and carbon tax tubes.'
£115 at Poshbikes. http://www.poshbikes.com/product.php?id=5