Dear friends, thank you very much for liking our products. All the marked product dimensions are the dimensions of the cylinder inner diameter. All products are made of molds, so there is a slight error between each product. The error range of each product is 1-3mm. How Do Pump Traction Devices Work? This gentle ,painless stretching causes the cells within the corpora cavernosa to pull away and split.Just like muscle buliding,during the cell healing process,healthy new cells are created,allowing your penis to become larger.And with a bigger corpora cavernosa,your penis can hold more blood,meaning you'll also enjoy bigger and harder erections!