Don’t buy this type of lens cap without trying it out. It does not fit on all lenses of the size indicated.
This was my second ill-fated purchase at the photo store on the same day I bought the useless lens Cap Keeper. This also turned out to be useless.
My lens says on it clearly 55 mm. This lens cap says both on the package and on the inside of the cap itself, 55 mm. It’s simple. You just push in on the spring-loaded sliders on the edges. The little rim then will fit inside the edges of your lens and the pressure of the springs holds the cap in place. But the rim of this cap does not fit inside the edge of my lens. There was no warning at all that it might not fit on all lenses.
The main lesson is to not buy stuff like this far from home. I didn’t get back to that city again until way too late to return the item. And although the other loss was only $2.49, this one was $6.60, so all together I learned a lesson that cost almost $10, which begins to sound like real money.