Needle tips are usually sold by pin count: 9, 11, 12, 16, 18, 24, 36 and 42 are among the most common. Lower counts concentrate the work in a smaller footprint; higher counts cover more area per pass. Clinics and trainers often keep more than one count in stock so operators can switch by protocol — not because one count is "better" in every case.
Nano tips (round, S, 3D and similar labels) use a dense array of very fine points or a silicon-style face. They are listed separately from pin-count tips because the feel and intended use differ. Stock both families only if your buyers ask for them.
When you place a wholesale order, treat each specification as its own line with its own minimum quantity. Mixing pin counts in one line is not supported — select each tip separately so packing and pricing stay clear.