Ultra rare, only one I've ever seen!  Post war M1918a2 receiver wrench.  tag reads:

M1918a2 cal.30 B.A.R

Wrench, Receiver (41-W-1998-625)

(6316005) New. . .

Stamped on the head is the # 6316005

USGI and appears un-issued.  I always though this more of a collectable rarity than a usable item, although it's totally functional (I always used a padded bench vice for the receiver and a custom built barrel wrench for my builds)