The type of stopper you will choose to use for your vials all depends on the type of medication content in the vials. Serum vials come along with rubber stoppers, plastic and silicon stoppers. The rubber stoppers are good because they are elastic and can fit any size of a glass neck. If you want to have the exact fitting stopper for your vials then you can use the plastic or silicon vials. It is only to ensure that the content of the vials are not going to spill neither are they going to mix up with impurities or air.