Since the restrictor orfice in the filter canister standpipe is only 1/16" in diameter, whatever line you've got handy will probably work OK. The original equipment rubber flex lines that came with the dealer-installed filter had about a 3/16" inside diameter, so 1/4" hard line will be more than enough. If you're going to plumb the filter with metal tubing, be sure the canister is mounted to the intake manifold, not the inner fender. Engine movement under torque load would fatigue a metal line and eventually cause a leak and possibly a catastrophic engine failure due to running out of oil. Some people like to put a 360 degree vibration loop in a hard line installation to prevent fatigue failure, but that might be just a bit of overkill.
Jerry

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