[Practical Threaded Inserts Kit]: M2.5 x 3.5 x 4 kit contains 100 fusion threads with M2.5 internal thread, 3mm in width and 4.0mm in length. M4 x 6 x 8 kit contains 50 fusion threads with M4 internal thread, 6mm width and 8mm length. [Secure hold with easy operation]: Helical knurled nuts provide balanced high tightening torque and ensure a stable connection. [High quality brass, corrosion resistant]: This threaded insert is made of high quality brass. It is manufactured using Hotmelt technology and has excellent properties such as high temperature resistance, waterproofing and impact resistance. It is also sturdy and durable. Even if it stays in a humid environment for a long time, it does not react chemically with substances in the air, resulting in rust or loosening. [Smooth polishing and good thermal conductivity]: Each nut printed 3D with threaded insert in this product has been carefully polished and has no burrs on the surface. Copper has good thermal conductivity, which not only makes the copper nut heat up quickly and accelerate the work efficiency, so that the thread can be 3D printed more easily in the hole.[Application]: Insert the threaded nut into the hole and heat the nut with a soldering iron. After heating, the threaded insert is pressed into the workpiece. Then the screws are mounted with the cooled nuts. Using ultrasonic waves or a soldering iron, nuts can be easily inserted into plastic parts.