Sometimes women, trans folks, and femme of centre people will use breast pump cylinders in conjunction with hormones to change the size and shape of the breast. Pumping regularly (e.g. 1/2 hour a day each day) will increase blood flow, and stretch the skin to help change and develop the area. Additionally, sometimes folks will use breast pumps before having breast surgeries. These breast pump cylinders are an exciting addition to our selection of USA made LA Pumps products. The medium cylinder measures 3 7/8"" at base; the large measures 4 7/8"" at base and the xl measures 5 3/4"" at base. Sold individually. Made of acrylic.