M14x1.5. It's an Asian transmission, so don't go thinking that it's going to be a regular "inch" thread.
You could probably take it up to a pipe thread - but it would be at least 1/2"NPT. For that, you'll have to drill out the hole a little larger (I don't think there's a pipe thread that will work from a 9/16" or 14m/m hole.) I think 1/2"NPT will astart with a 5/8" hole - but that's something that would have to be checked. You might want to at least remove the valve body and set it aside before drilling those holes out - you can remove it without taking it to bits, tho.
If you go that route, you shouldn't have too much trouble finding a 1/2"NPT to -6AN adapter, and you can find hose barb fittings in -6AN for 3/8" hose all day long (check for a local Parker-Hannifin Fluid Power Systems dealer, or similar.) The -AN adapters would be permanently installed, and anytime you'd need to remove the hoses you'd just pull the -AN fittings off the adapters. Keep a couple of -6 plugs around, and if you're quick you won't drain the lines if/when you disconnect them (that's how I do it.)
Failing that, you're in for a larger job that you're probably ready to tackle. Consider yourself edified...
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