The choke cross-sectional area, i.e. the cross-sectional area of the ingate, is designed according to the choke section method. After the cross-sectional area of the ingate is determined, the cross-sectional proportion of each unit of the gating system of sand castings and its application are shown in the table.
| A straight | A horizontal | A inner | Application |
| 1.4 | 1.2 | 1 | Sand casting of medium and large gray iron castings |
| 1.15 | 1.1 | 1 | Medium and small gray cast iron castings |
| 1.11 | 1.06 | 1 | Sand casting of thin-walled gray iron castings |
The reducer box body sand casting is a thin-walled casting, and the proportion of the minimum sectional area of each unit of the gating system is in accordance with
A straight: A horizontal: A inner = 1.11:1.06:1 calculation.
The proportion of interruption area of mid injection and stepped gating system for sand castings is
A straight: A horizontal: A inner = 1.11×5.844:1.06×5.844:1×5.844 — 6.94:6.19:5.844
The proportion of interruption area of top injection gating system for sand castings is
A straight: A horizontal: A inner = 1.11 × 9．45：1．06X9．45：1 × 9．45=10．49：10．01：9．45