This is the cover to a light that is installed in my shower. NB. I do not attest to the fitness of this particular arrangement for a shower. Be responsible for your own actions.

Anyways... you'll notice two things in the pictures: the spring-things and the translucent bit of ceramic that the light shines through. The springs clip into a pair of notches up in the light fixture. The springs are held on by rivits in the original and by M5 20mm bolts with fender washers here.