At that time Yahweh said to Joshua, Make you flint knives, and circumcise again the children of Israel the second time.
We have discovered no reasonable explanation of why "flint knives" were used for the circumcision reported here, other than the obvious fact that it seems to have been traditional.  Although, we do not trust the Septuagint (LXX) with any great credibility here, it is written therein that, when Joshua was buried  (Joshua 24:30), "They put with him into the tomb in which they buried him, the knives of stone with which he circumcised the children of Israel at Gilgal."[13]