The muscle or body part you will inject into is not the only deciding factor of which size needle to use, there is another, that being, what type of liquid you intend to inject.

The thicker the liquid, the larger the needle gauge is required. If injecting a thick oil based substance, the smaller the needle, the much longer it will take to draw the liquid from it's container, and also to inject it into your body. For example, using a small 30g needle to draw an oil based liquid into a syringe is virtually impossible to do, much less injecting it into your body.

For newcomers, the needle gauges/sizes might sound confusing. However, simply put, the larger the number, the smaller the needle. For example, a 23g needle is much larger than a 30g needle.

Our recommendations are:

For water based liquids - Any needle size will suffice.
For oil based liquids - Use nothing smaller than a 23g needle.