These glass pipettes are an herbalists and aromatherapists staple for dispensing liquids and tinctures from glass bottles. Clear glass pipette attached to a black bulb. The line of glass droppers offered by Mountain Rose Herbs are threaded to fit the line of amber bottles that we offer, and most of the cobalt bottles that we have. The 4 oz droppers will not fit on our 4 oz cobalt bottles. Please note that the 1/2 oz, 1 oz, and 2 oz droppers are not compatible with our amber reducer bottles. We do not recommend storing these droppers in essential oil bottles as the bulb will degrade over time.