This is an alternative hand grip for an airsoft mp5k. This style of hand grip was popularized in the video game "Call of Duty: Black Ops" where you can use one of the earlier versions of the Mp5k that featured this different front hand grip.
Originally this is what the first Mp5k's hand guard looked like when H&K designed the weapon back in 1976. It was meant to protect users fingers from getting accidentally blown off, but was latter changed to the more widely recognized bulbous shaped hand grip.
This replacement grip has been tested with a Tokyo Marui Mp5k but should fit a wide variety of different manufacturers guns, without any modification, though I cannot guarantee it!
Simply order the part from Shapeways, wait till it arrives, spray paint it a matte, or textured black, and install on your Mp5k using the existing retaining pin!