10mm bar extensions for mountain bikes. Increased my bar width from 740mm to 760mm. These are only for use with lock on grips that have the lock on the inside of the grip, for example the Ergon GE1 grips. You don't want to lock anything onto this extension.
There is a 7mm hole in the inside of the extension, if you remove the grip and the extension get stuck inside you can use a bit of 8mm threaded rod or "all thread" or just a long 8mm bolt to screw into the extension to remove it from the grip.
The bars picture are Renthal Fatbar Lite