This original Nikon part allows older, prong-style lenses to be modified for compatibility with the AI (Auto-Indexing) metering system. This ring is designated No. 72. Several other rings are also available. Ring No. 72 is for use with some Nikkor 80-20mm f4.5 lenses. Serial numbers are 210001 and later, but please be advised that this lens, in this serial number range, still could take three different rings, of which No. 72 is the middle size. Sadly, there is no definitive way for us to know which you need, and this ring is not returnable.
Please be sure that all repairs are carried out by a qualified technician. Let us know if we can help you with your repair needs - we are a full-service repair facility. And if you don't find the ring needed for your lens, we can modify the ring that came with your lens, too! See our listing for Nikon lens AI conversion service.