The size of the needle is marked by the letter "G" and a number. As the needle gets thinner, the resistance to insulin flow increases correspondingly, which results in slower infusion speed. At this time, larger injection force is needed to reach the original infusion speed. Currently, there are new technologies that increase the inner diameter of the needle by keeping the outer diameter of the needle unchanged, that is, reducing the thickness of the tube 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-flow needles (ultra-thin walled needles). Pain, bruising, fluid leakage, and skin irritation with thin - walled needles were mild compared with normal - walled needles. In particular, it is more suitable for diabetic patients due to lower pressure, shorter injection time and less pain.