These are cool

[Matttoadman]

It's a shame these are so high. These are instant vent covers for our roach bins.  https://www.amazon.com/Gear-Aid-Bug-Mesh-Repair/dp/B00MKXCAEY/ref=sr_1_27?ie=UTF8&qid=1499648481&sr=8-27&keywords=no-see-um+screen

 

[stanislas]

Very nice option! If one can find a Chinese supplier that sends 25 of these for 5 dollar... 

 

[Redmont]

Check out roundvents.com and click the section that says, Aluminum open screen vents - tab style, they have all different sizes and the 3 inch vents are only $1:65 a piece. I bought a box of them last year and I'm still waiting to throw them in some cages