Brembo M6 bleed nipple (8mm spanner size, fits many rear calipers, and is also fitted to some later bikes where it screws into the brake line banjo bolt).
Please consider also the Stahlbus bleed valve BRA10111 to make the job of bleeding your brakes easier!
These can often snap when attempting removal from R1100, R1150 and R1200C rear calipers; please see SSA00475 for a stainless steel replacement nipple holder, and BRA12111 for a Stahlbus replacement for both the holder and the nipple.