There's nothing like having the right tool for the job.  These are just right for tightening or loosening the retainer ring on sight glasses.

The smaller one is for sight glasses with an overall diameter of 60-90 mm, which is about 2 3/8" to 3 1/2"

The larger one is for sight glasses with and overall diameter of 90-155 mm, which is about 3 1/2" to 6 1/8"