After a few years partly desperate searches for misplaced lens caps I have now resorted to a product with a cord for tying. The cord is long enough that the lens cap fits on long lens. When changing lenses, the cord must indeed be threaded, but that bothers me less than the constant search in trouser and jacket pocket, the photo backpack, etc. after each the lens cap.
CONCLUSION Would I buy it again at any time (hopefully not necessary, because now I should not lose the lens cap ...)
