M7 thread male elbow push in fitting from Pneuflex can match 4mm, 6mm, 8mm, 10mm, 5/32", 1/4", 5/16", 3/8" O.D size tubing.
https://www.wellfittings.com/composite-push-in-fittings/composite-push-in-fittings-for-metric-inch-tubing-pt-r-bspt-connection-thread/