Syringe question

[sco44]

Hello I was hoping some one could help me I think I know all the parts to a dental syringe but what is the part that goes over the syringe its self its metal with a curved needle its been on my mind and how is it cleaned.? I have never found it on a internet search, you would take it off to refill the cartridge i saw a
dentist i went a 3years ago do this.

Thanks. any help would be greatly appreciated