HCA: Hermit Crab Association

I bought some of them off of amazon, and I wanted to know if these are safe: http://www.amazon.com/gp/product/B0000C ... ge_o00_s00

They are metal, but they are going to be mounted at the top of my tank with the hemp net that I have. If they aren't safe can anyone suggest where I can buy one thats safe for them?

Thanks.

I'm not sure about safety, but if you end up needing to buy other ones, you can get plastic ones like these http://www.amazon.com/Plastic-Suction-H ... uction+cup I have some similar ones that I think I bought from Menards.