Ice Maker Tubing from Wall Size? | Terry Love Plumbing Advice & Remodel DIY & Professional Forum

I am attempting to install an ice maker shut off box behind my friends refrigerator. There is ~2 feet of black tubing protruding from a small hole in the wall, and the same tubing is coiled up under the sink. I measured the tubing with a caliper, and found it to be .360" OD, and .250" ID. So it is neither 3/8 or 5/16. Anyone come across this?

Thanks in advance.