Shower fixture loose

[MrsSilenceDogood]

The plastic cover does not fit tightly over the nut. How do I fix this?

The nut also does not fit tight to the wall. Is this normal?

 

[freddiemercurystwin]

Bit of silicone.

 

[MrsSilenceDogood]

Thanks for the advice. Out of interest, is that part simply called a nut, or is there a more accurate term?