This gear fits the Nikon Nikkor 50mm f/1.8 Ai-S lens.

It’s specially designed to fit this lens and is compatible with any standard 0.8 Module follow focus unit. Focus gears are generally slim for a clean, low profile gear that slides smoothly onto your lens and into your current lens case. Custom spec gears can be made on request. The gears do not have to be removed after each use although you can if you like. Each gear comes with a lifetime of support.

This gear is very specific to this version of the lens. The Nikon AI-s, AI, and pre AI lenses look very similar. You can double check which version of the lens you have by serial number here:

http://www.photosynthesis.co.nz/nikon/serialno.html

50