Glock G17 33 round magazine - black follower.   Retails for $40 - selling brand new in original packaging for $20. 

Product Description:  These Glock factory original, drop-free extended magazines fit your Glock double stack 9mm pistol, for instance the Glock 17, 19 and 26. Fits all generations. Should work with any aftermarket firearms that use Glock pattern double-stack 9mm magazines as well. These Glock magazines have a hardened steel insert encased in high tech polymer. This polymer coating protects the magazine and prevents deformation, even when dropped from a great height.

Note: These Glock magazines are compatible with previous and current generation Glock pistols. Follower color and generation is irrelevant.