The needle of any syringe used with the Mini GC should have an outer diameter of 0.5 mm or 0.019 inch. This is a 25 gauge needle size.

It should be inserted 1.5 inches into the injection port of the Mini GC. The syringe that Vernier ships with the Mini GC and sells separately has a 3 inch needle, but also includes a needle guard that only allows 1.5 inches to be inserted.