Description from KEH:

EXTENSION RING SET K consists of a set of 5 rings which can be used individually or in combination.

For close-ups from 1/8.9 to 1x with a 50mm F/2 lens.

Rings fit between the camera body and lens and accepts any Nikkor lens, 20mm to 300mm.

Non AI. I'd be willing to guess that it should fit other micro Nikkor 50mm lenses, such as the f3.5, but I am not positive.

In excellent condition. Comes with original leather case.