ABBCO's Kantleak™ shut-off valve has 1/8" NPT pipe thread inlet and outlet and is rated at 1,500 PSI. The handle can be removed, and you can mount the shut off valve to a tab with a 9/16" hole.
Cross reference Allstar Performance part number ALL48010 or Parker Hannifin 2F-MB4LPFA-BP
More than 8 available, and at discount for multiples.