Which needles for hand stitching - Sewing Leather

I’ve read that size 4 and size 5 harness needles are the most common needles to use for saddle stitching. I ordered some CS Osborne # 517-4 and 517-5. Did I get the wrong needles? What should I have gotten?

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John James Saddler's Harness Needles - Ohio Travel Bag 16 (3/0)

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