TL;DR: You can mount this lens on a Nikon DSLR only with a "speedbooster" lens adapter.
The "MC" in the picture indicates this is a Minolta MC/MD mount lens.
seller says fits canon 49mm. won't fit my camera since I have nikon D5500 which I think is 52mm
I think the seller doesn't know what they are talking about. The "⌀49mm" means the lens takes 49mm filters.
Minolta MC/MD lenses won't fit on either Canon or Nikon cameras without a "speedbooster" adapter. This is because the registration distance (also sometimes known as flange focal distance, such as at Wikipedia) of Minolta MC/MD mount is 43.5mm. Canon's EF/EF-S mount FFD is 44.0mm, and Nikon's F-mount FFD is 46.5mm. Any adapter to mount the Vivitar lens to either Canon or Nikon DSLRs will probably be add at least 5mm or more of depth, which would put the Vivitar lens too far away from the Canon or Nikon body.
If you wanted to mount this lens to a Nikon F-mount DSLR, you'd need a so-called "speedbooster" (it's a mount adapter that has a refocusing element in it, to allow the Vivitar lens to focus to infinity when mounted further from the body than the designed FFD). For example, Fotodiox sells such an adapter for around $40 USD.
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