## 4 Discussion  
In the production practice, the above four kinds of structure of the tie rod each has its best application scenario. The structure of A, B and C are mature designs, which have been widely used in the past non-standard magnets and common standardized MRI, MCZ and other magnets, and their performance is stable. The difference is that the application scenario of each structure is different, the best range of the tensile force they adapt to is different, the structure is not good or bad, and, relative to the type D tensile rod, is only poor in versatility; once the production is completed, the length and maximum tensile load cannot be adjusted. Rods with a tensile load rating of more than 150 kN are mainly used to suspend large mass 4 K temperature zone components, especially in large magnet systems with fewer rod numbers (such as accelerator magnets with a cold mass of more than 20 tons). Large magnets are equipped with high-power G-M chillers, which are less sensitive to pull rod conduction heat leakage. A racetrack rod and cylindrical rod can use a CFRP rod body with a large cross-sectional area to meet the high tensile strength requirements. If the type D tie rod design idea is adopted, it is necessary to increase the number of single tie rod branches, \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Actual Maximum Tensile Load (Unit: kN)**} \\ \hline Number & Type A & Type B & Type C & Type D \\
1 & 183.33 & 144.96 & 148.92 & 146.91 \\
2 & 179.58 & 145.23 & 149.75 & 148.16 \\
3 & 178.46 & 143.77 & 147.77 & 147.73 \\
4 & 181.79 & 146.25 & 148.36 & 147.69 \\
5 & 180.64 & 143.97 & 146.98 & 146.88 \\
6 & 178.55 & 144.31 & 147.59 & 148.19 \\ Average & 180.39 & 144.74 & 148.23 & 147.59 \\ Effective cross-sectional area (mm\({}^{2}\)) & 90 & 90 & 78.53 & 75.40 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Maximum tensile force that samples of four types of rods after tensile testing. increase the diameter of single branch rods and increase the number of tie rod groups to meet the requirements of the cold quality of fixed magnets, which will significantly increase the difficulty of manufacturing and assembly of metal chuck, as well as the cost. Drawbars with tensile loads rated between 10 kN and 150 kN are commonly used in medium magnet systems, such as 1.5 T and 3 T full-body MRI magnets, with cold masses generally not exceeding 10 tons. The type C tie rod is simple, stable and reliable, and although it does not have the adjustment function, it is very suitable for the design of mature commercial magnet systems requiring mass production. In contrast, the design idea of the type D tie rod is more suitable for the development of new superconducting magnets, the small batch production of special magnets and the maintenance of old magnets. In these applications, the D rod allows flexible adjustment of the number and length of the branch rods, which is particularly suitable for scientific institutions and limited companies without carbon fiber impregnation and baking equipment. A tie rod with a tensile load rating of <10 kN is typically used in small magnet systems with a cold mass of less than 1 ton, such as MRI magnets for small animals or joint scans of limbs. The installation space available inside such magnets is very limited. The racetrack-type tie rod structure of type B tie rod structure is simple and easy to miniaturize, and the stress concentration in the arc part of the rod body is acceptable under low load, so the type B tie rod structure is often used in small magnets. Although the diameter and number of branch rods can be increased to increase the rated maximum tensile load, the cost will be greatly increased and the rod of type A can easily increase its effective cross-sectional area to bear a larger load; although its geometric size is larger, it is usually used for magnets with larger internal space and larger overall size. This could be seen as a kind of limitation of this design.