[jeff5614]

It's ID. Using some on my fluval's also.

 

[jeff5614]

I've only used straight tubing to connect my reactor and UV to the filters and it does connect to the filters using the lock nuts with no problems. I still use the ribbed tubing from those two pieces into the tank. Eheim supplies a fitting with their filters that keeps tubing from kinking at the bend into the tank which I would imagine you can buy seperately. You can see it in this post.

http://www.plantedtank.net/forums/equipment/71660-eheim-hose-sleeve.html

 

[jeff5614]

Forgot all about the fluval ones.