I'm still weighing the options with the halide, but probably looking at a clamp-on due to heating issues with the stock hood.
As far as the loc-line goes, you should be able to measure what you need yourself, you can pm to marybebo on here, I believe she used the loc-line. It looks to me like their measurements are I.D. so you'll want to check the O.D. of your output to decide what you'd need I guess. I think mary said that whoever she bought from actually put them together, eliminating the need for pliers. You might want to check out her thread.
I myself would prefer to drill a second hole and split off the pump in the back using a Y, that way the two returns are less visible than with the loc-line. But, if your tank is already full, i'd look into the loc-line for sure, or if you have a 24g maybe. Only because on the 12g two seperate returns from the back wall will probably be effective in creating enough flow around the tank, but the 24g is larger, so you might want to move the loc-lines around to find a good flow.
Home Depot is useless! I didn't find any barbed fittings at all, all I came home with were some buckets, tubing and epoxy. Still need a slip fitting, a Y split and some aquarium silicon. *sigh*.
-A