We had a long conversation about this topic earlier in the thread, I posted the P&C WWII contract records, and I started a running list of examples found. Empirically, there are actually more of the N- series DBE wrenches than WF- wrenches, fewer socket drives tools, though, so far. Also, the length specs are different. But the sizes DO correlate to the same part numbers. The most interesting thing is that the N- series wrenches imply that the WF- series numbering scheme probably came from Plomb, not the Air Corps. Because P&C used the same system for a completely different technical branch (Navy). See pages 19-22. Don was involved in tall that. I think he is hedging because we don't have anything that directly indicates that the P&C Navy contracts produced the N- series wrenches. The thing is, we don't anything like that for the Plomb Air Corps contracts correlating to the Wright Field (WF) wrenches, either. That, too, was only inference. Big difference is the Navy N- series is far less acknowledged, let alone as popular as the Air Corp WF- series.