"Russell Duffy" <13brv3@bellsouth.net>:

"""
 My current oil system started out as AN12 all the way, but I ended up having
 to use an AN10 fitting at the engine, so the lines change from AN12 to AN10
 along the way.
...snip....
 Rusty (I know bigger is better, but AN10 is going to have to do)
"""

Here's a data point for you, Rusty.  On the Eagle we use AN8 for the oil presssure lines (between engine and oil coolers) and AN10 for the returns. The pressure side can typically be smaller than the return, something about flow under pressure vs flow under suction.  Ditto for the coolant lines... 1.25ID for pressure, 1.50ID for suction.  I thought you'd be interested.

 <marv>