Question about using an Insulin Syringe to measure mls

Thanks for your answer, but what I guess I want to know is can you measures parts of mls in a 1ml Insulin syringe that is labelled units? We give shots made up of .33mls, .5, or .66 mls at times. Aren't these a different measurement than units? How would you measure that on a syringe that is marked units? Still need some input.

In response to my latest answer if we can use the insulin syringe to measure up mls. I believe my situation is a little different. We use Sub Q butterflies and draw up very small amounts of morphine from either 10mg/ml or 15mg/ml multi-dose vials. We are not using IVs for administration or normal saline. We draw up small amounts such as .33 = 5mg, or .5 = 7.5mg, etc.. and this is injected via a butterfly that is left in. That is why I am questioning measuring this with units as the measurement vs. mls on the barrell. It makes sense that 50u = .5 of a ml, however, can you measure in between these measurements safely? I would appreciate more input on this matter. So, the new question is: can you measure mls the same as units no matter what amount you need under 1ml safely?