What size needle should be used for the deltoid muscle an adult male?

The deltoid muscle is a relatively large muscle, so a larger bore needle is typically used for injections into this area. A 1 inch, 22-gauge needle is typically used for adult males. This size needle is long enough to reach the muscle, but not so long that it would cause undue discomfort. The 22-gauge needle is also small enough to minimize pain and discomfort.