The basic parameters of automobile steering gear mainly include the number of teeth, modulus, pressure angle, tooth width, displacement coefficient and other basic parameters.
According to gb1356-88, the standard value is: Ha = 1, C = 0.25. Through these parameters, the radius of indexing circle, base circle, tooth tip circle and tooth root circle can be determined, so as to realize the drawing of steering gear. The main parameters used in the modeling process are shown in the table.
| Name | Parameters | Formula | Type |
| Number of teeth | Z | Integer | |
| Modulus | M | Length | |
| Pressure angle | A | Angle | |
| Helix angle | Beta | Angle | |
| Tooth width | Depth | Length | |
| Displacement coefficient | Xn | Real number | |
| Dividing circle radius | R | R = m * Z / 2 / cos (beta) | Length |
| Radius of addendum circle | Rk | Rk = R + M + Xn * M | Length |
| Radius of tooth root circle | Rf | Rf=R-1.25*M | Length |
| Radius of base circle | Rb | Rb=R*cos(A) | Length |