advice needed on viewfinder diopter lens

[E. von Hoegh]

It will fit most any Nikon from the F onward. Use the fingernailpolish trick, or if you wish to go "retro" use a tiny dab of boiled linseed oil.

[Neanderman]

...if you wish to go "retro" use a tiny dab of boiled linseed oil.

Or shellac, which is very easily dissolved with alcohol.

Ed

[E. von Hoegh]

Or shellac, which is very easily dissolved with alcohol.

Ed

Personally, I like safety wire. Locking tabs are good, too.