SILBERBRAND, Boro 3.3. DIN 51368. Interchangeable hollow glass stopper size 19 / 26. Calibrated to Contain (TC, In). For determination of oil content in aqueous oil emulsions (e. g. drilling oil). SILBERBRAND, Boro 3.3. DIN 51368. Interchangeable hollow glass stopper size 19 / 26. Calibrated to Contain (TC, In). For determination of oil content in aqueous oil emulsions (e. g. drilling oil).