If you look at enough gas spring tanks you will notice that the large end (which attaches to the base) is tapered which makes it fit snugly to the base of your chair. The length of the constriction varies depending on the cylinder. An important measurement is the distance from the beginning of the constriction to the tip of the thin end. For this product, that size is 14 inches, but the photo shows it is 14 inches from edge to edge. It is not true. The actual product is approximately 1 inch longer (cone length) and measures approximately 15 inches. Also, the product seemed to work fine for the few minutes I spent in the chair before I returned it because it was too high.