Straight plug style stoppers provide maximum sealing for vials with straight wall glass finish. The straight wall interior finish is typically found in vials from European manufacturers. This style is not recommended for vials with a blow-back feature, which is a small ridge on the interior of the vial's neck.

Snap-on style stoppers provide maximum sealing for vials with a a blow-back glass finish, which is a small ridge on the interior of the vial's neck. The snap-on stopper locks into the blow-back ridge, providing a tight seal and keeping the stopper from backing out. This style is not recommended for vials with a straight-walled finish. The blow-back feature is typically found in vials from North American manufacturers.