The mesh I used for my Gerbil Topper was the 1/4 inch grid. It’s not as strong as 1/2 inch. I didn’t use 1/2 as I didn’t want them to be able to get their muzzles through it and start chewing habits. However, due to the need for them not to slip through the door and sides of the entrance I use spring loaded hooks and the tightness was causing the mesh to begin bending. And the door was floppier as well. I just became unhappy with it and did not feel it was secure enough. I was always afraid the mesh would eventually break causing the hook latches to come attached and therefore come home to missing gerbils. Ugh. The thought horrifies me.
So, I bent a section of 1/2 mesh in half and put the hard plastic borders around it (Totally blanked on what those are called! – The red things around the frame) and attached it. It’s so sturdy that I only need two spring latches opposed to the four I needed with the other door. And the way I folded the piece makes it a little difficult for them to get their muzzles through. And even if they could this mesh is very strong so they couldn’t gnaw through it if that’s even possible or desirable for them to try to do. It looks cleaner to me. I’m pleased.
*Other additions – I took the two sides off the burrowing box and flipped over the little steps and turned it into just another shelf for them to climb on. In the middle is just free space with no walls. Only walls are on the sides facing and the back to stand it up.