Thanks bentleya. Also nice to have comparison measurements on the contenders.

@IFMU - boy, your questions made me feel good. I struggled for weeks before ordering compression fittings when they started to become the rage - because I had no idea how they actually worked. It's a lot easier to explain with a photo - and maybe bentleya will post one. But the simple explanation is, there are two parts - the barb and the collar. The main body screws into the water block/radiator/pump G1/4 opening. The "naked" fitting now looks like a regular barb - you can see it in the middle of the first comp fitting in bentleya's photo no. 1. The tubing goes over the barb just like normal. The collar (don't know the right term) slides over the tubing and then you screw it down to hold the tubing in place.

That's why it's important to get compression fittings with the proper ID and OD.