Thing is, even if you fit 1/2" barbs on an Aquatube, you're dealing with a restriction at the threaded end as it is a 1/4" thread. Instead, I just drilled out my Aqua-Tube thus:
to accomodate it for 3/8" ID tubing --that's a 3/8" BSP thread barb in the side. This tubing will fit over 1/2" barbs, by the way, if you warm it up first (just dunk it in some hot water for a few minutes, else use a hair dryer), and make a nice, tight fit.
Many 1/2" barbs, when you measure them, turn out to be only about 10mm (3/8") to 11mm ID, so in terms of restriction, using 3/8" ID tubing instead of 1/2" is not, I imagine, a biggie.
The barb in the bottom is a 3/4" ID barb (this is an Aquatube v1.0 which did not yet have three 1/4" bottom barb holes). This runs straight to the pump inlet. I deliberately chose a bigger diameter tubing for the res --> pump inlet connection to prevent restriction and cavitation. As such the setup looks like this:
I have made a modification since; different pump (and hence a different bracket):
And various other things besides. The whole thing, by the way, is a Dual Athlon MP 2800 in a Lian-Li PC-12.