Nozzle, timing gear oil is correct. Some plates I believe this is a tube pressed or welded in, not threaded.
Used is probably where you’ll find one.
Part number for threaded type with 1/8” nozzle is 3690722

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-