These 500 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.