[Gooserider]

Many cores have the larger diameter tube made by flaring out the smaller size, as was mentioned earlier. It is easy enough to cut the oversized bit off, along with any excess tubing. It is then possible to apply barbs to the remaining stubs. Get a size intended to fit over copper pipe the same size as the OD of the tubing coming out of the rad. (You should be able to get these at a hardware store or Home Depot, but you might need to go to a plumbing supply store)

The best attachment method is to solder (NOT weld!) them on, use a propane torch, low temp (lead, not legal for drinking water systems) solder, and acid core flux. I reccomend filling the core w/ water to keep the heat from getting into the rest of the core and desoldering things you don't want desoldered.

If soldering isn't possible, or it is an aluminum core (don't use copper fittings on an Al core) try JB weld, plumbers goop, or other waterproof sealant/adhesive intended for continuous immersion.

Whatever method is used, pressure test when done (25 PSI max) to ensure there are no leaks.

Gooserider