Help to translate Tunisian dagger

[ShakaAmaZulu]

Hello,
Please could you translate arabic words on this Tunisian dagger ?
Thanks in advance

[kwiatek]

It is something like

سلاح نافع للعدو دافع

"A useful weapon, it repels the enemy"

There is an extra letter in it I cannot make sense of, someone else may be able to do better