The new Brompton "Spider" crankset was introduced on new Brompton bicycles at the beginning of 2013.
This is a replacement 50 tooth chain ring complete with guard - BLACK edition
Note: This is just the chain ring / guard, and doesn't include the pedals / cranks etc
It can be used to replace the 44, 50 or 54 teeth chain rings on a "spider" type crank.
A standard 3 or 6 speed Brompton comes with a 50 tooth front chain ring (this size)