Question on Nambu type 14

[Flyboy73]

I have a Nambu type 14 and have a quesion on it. On the back of the grip, there is a metal strip forming a half circle on the grip.

See middle picture

http://www.auctionarms.com/search/displayitem.cfm?itemnum=7208191.0

Any idea what that is for. In other Nambu pics i don't see it.


Brion