The screw is a cylinder with a spiral groove cut on the outer surface or a cone with a tapered spiral groove. The design principle of the full-thread screw is introduced below.
　　The main part of the full-thread screw is an ordinary screw, which can be set in the melting section of the screw or the drop groove of the metering section or the smooth cylindrical surface without screw grooves at the end of the metering section. Set according to a certain arrangement, the density and the quantity can be varied. The cylindrical pin is formed by assembling the pin into the hole of the screw; the square or diamond-shaped pin is formed by milling the pin directly on the screw.
　　The mixing section is an inwardly slotted structure at the end of the homogenizing section of the full-thread screw, and its outer diameter is equal to the outer diameter of the screw. The groove is divided into several groups, and between each group is the confluence area of ​​materials. The materials are divided by grooves, and then they are divided and merged in the confluence area.
The characteristic of the separable full-thread screw is that in addition to the original screw pattern (called the main screw), there is also an additional thread (called the additional thread) on the melting section. Its outer diameter is slightly smaller than the outer diameter of the main thread. The lead of the pattern is different. The secondary thread starts from the end of the feeding section (and is connected with the feeding section here), and after several threads, it gradually intersects the main thread of the homogenization section.
　　The depth of the groove and the thread lead of the full-thread screw are gradually changed from the feeding section to the end of the homogenization. That is, the thread lead gradually narrows from the width, and the groove depth gradually becomes shallower from the depth, which can maximize the compression of the material.