I've come across a few parts that have ND at the end of their part number on Mouser and DigiKey. I can order the part with the ND at the end or not. What does that mean?
I've never seen the ND suffix at Mouser, only at Digi-Key. According to a blog article at Skywired:
In those days, the “-ND” suffix meant No Discount. Prominently displayed on the catalog front cover was a schedule of discount percentages, with better discounts for larger orders. Full reels of parts and certain expensive items had an “-ND” on their part number to mark them as exempt from the discount, but anything without the “-ND” was fair game. Later, Digi-Key started listing price breaks for intermediate quantities (10, 25, 100, etc.), and as that practice spread through the catalog, the “-ND” suffix became ubiquitous. Today, it serves only as Digi-Key’s signature, which is ironic given its origins as an exceptional case.
Source: Farewell, Digi-Key Catalog
In essence, I think it has no significant meaning, and parts with and without that suffix that have otherwise identical part numbers are identical parts.