Are you sure it's 1/2" NPT you need?
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Only reason I'm asking, is that image is totally wrong if it is. 1/2" NPT has an OD of 21.6mm, whereas the M16 has an ID of 14.5, so the male threaded section should be larger than the female section.
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Have you tried hydraulic connectors?
I'd have a look, but all my hydraulic fitting catalogues are in the workshop, and I won't get anywhere near them until late tomorrow. How much room have you got, as it may be easier to go via BSP fittings.