The thickness of the needle is marked by the letter "G" and a number. G stands for number. As the needle gets thinner, resistance to insulin flow increases correspondingly, which results in slower infusion speed. At this time, larger injection force is needed to reach the original injection speed. Currently, there are new technologies to increase the flow rate by keeping the outer diameter of the needle unchanged and increasing its inner diameter, that is, reducing the thickness of the pipe wall of the needle to increase the flow rate without making the needle become fragile and without increasing the breakage and bending of the needle. The guidelines recommend the use of high velocity needles (ultra-thin walled needles). Pain, bruising, fluid leakage, and skin irritation with thin-walled needles were mild in patients compared with those with normal pipe-wall needles. Especially because of the lower pressure, shorter injection time, less pain, more suitable for diabetic patients.