Well, it's a standard fountain pen nib/feed/section thread but not exactly a standard thread. The JOWO and BOCK nib feeds use proprietary threads. The taps are made special order or from a couple vendors. You can't get them from the local hardware store nor most online places.
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You can get the taps (and I think dies as well) for JOWO nib housings from Mike Redburn at:
Silver Pen Parts
Bill