These 50 ml PYREX� Erlenmeyer flasks are designed with heavy duty rims to reduce chipping. Their uniform wall thickness provides the proper balance between mechanical strength and thermal shock resistance. Texas Residents: Under Texas State Law, this product requires a Precursor Chemical/Laboratory Apparatus NAR-120 permit to ship to a Texas address. After purchase, the seller will contact you via email to verify your permit. Failure to provide a valid permit will result in a cancellation and refund of your order.