Best gauge for oil injections are 23-25G which usually comes with 2 and 5ml syringes.
If you use needles with Gauge 21 or 22 there are more chances to have pain after injections.
Below is a needle Gauge Comparison Chart so you can know more about this subject.
To see full article with images click here:
https://www.gbnstore.net/articles-ne...hart-4980.html