Bottles have permanent white enamel graduations and marking spots. Caution: do not tighten caps immediately after autoclaving. Each bottle includes a Linerless, one-piece autoclavable polypropylene plug seal cap with drip-free pouring Rings. Glass bead indicates full capacity line on 500-mL size. . Optional red PBT caps and red ETFE pouring Rings are available for dry heat sterilization (180ºc), order separately. Heavy-duty borosilicate glass-perfect for storage, mixing, and sampling