hole for filter sock

[jjreeftank]

Can anyone tell me the size hole needed to fit a 4" filter sock just wondering if its 4" or 4 1/8"

 

[Jawbone flats]

I use 4" filter socks but they are the ones with the Rigid Plastic Ring already fused at the top of the sock...

anyhow I use a 3 and 5/8" hole saw - the rigid ring on the filter sock wont go through the hole. so I can just place the sock in the hole and the ring holds it up from going all the way through.

 

[bassintoo]

3 3/4" and the ring sits flush wont go thru.