Screw Gears: Technical Information
Characteristics∧ top
KHK stock screw gears come in modules 1 ~ 4, 10 to 30 teeth, and four materials: S45C, SUS303, CAC702 (formerly A BC2) and MC nylon.Catalog No. | Module | Material | Heat Treatment |
Tooth Surface Finish |
Precision JIS B 1702-1 : 1998 |
Secondary Operations |
Features |
---|---|---|---|---|---|---|---|
SN | 1 ~ 4 | S45C | — | Cut | N9 | Possible | Popular screw gears. Additionally, gear tooth induction hardening secondary operations can be performed. |
SUN | 1 ~ 3 | SUS303 | — | Cut | N9 | Possible | Suitable for food machinery due to SUS303's rust-resistant qualities. |
AN | 1 ~ 4 | CAC702 (Al BC2) |
— | Cut | N9 | Possible | made of aluminum bronze, these gears have excellent wear resistance. |
PN | 1.5 ~ 3 | MC901 | — | Cut | N9 | Possible | Light-weight products made of MC Nylon and can be used without lubrication. |
Selection Hints∧ top
Please select the most suitable products by carefully considering the characteristics of items and contents of the product tables. It is also important to read all applicable “CAUTION” notes before the final selection. Since screw gears come in right- or left-hand helix, make sure to include the letter "R" or "L" in the catalog number when you order.
1. Caution in Selecting the Mating Gears
Screw gears are used for offset shafts. Whether the shafts are paralleled offset or skewed offset depends on the helix hands of the mating gears.
Direction of Shaft | Arrangement of Helix Hands |
Skewed Shafts | RH-RH or LH-LH |
Parallel Shafts | RH-LH |

Trusted Quality Achieved by Years of Experience.
Efficient production by lapping cutting processes
Gear cutting by a hobbing machine
Efficient production by lapping cutting processes

Application Hints∧ top

*The illustration above is a design example, not a design for machinery or a device in actual use.
The allowable surface strengths listed in the product pages were derived using the Niemann formula as reference values (for the case of skewed offset shafts).
There is scarce amount of data on the strength of screw gears. The values of constant K0 used in the calculations, which depend on the material of the mating gears, are our estimates. The mathematical expression below shows the Niemann formula to determine allowable tangential force F t (kgf) and allowable torque T (kgf • m) on a basic circle.
The Niemann Formula

Value of fz
Z2 | Z1 |
|||||
10 | 13 | 15 | 20 | 26 | 30 | |
10 | 1.538 | |||||
13 | 2.005 | 1.538 | ||||
15 | 2.279 | 1.786 | 1.538 | |||
20 | 2.963 | 2.329 | 2.053 | 1.538 | ||
26 | 3.695 | 2.963 | 2.588 | 2.005 | 1.538 | |
30 | 4.161 | 3.350 | 2.963 | 2.279 | 1.786 | 1.538 |
K0 values depending on material combination
Catalog Number |
Mating Gear |
K0 | The maximum allowable sliding speed m/s |
No. of teeth of mating gears |
Rotation |
SN |
SN | 0.0030 | 2.5 | Same Number of Teeth |
100 rpm |
SUN |
SN | 0.0030 (Note 1) |
2.5 (Note 1) |
||
AN |
SN | 0.0050 | 5 | ||
PN | SN | 0.0030 (Note 1) (0.0021) |
2.5 (Note 1) (1.0) |
(Note 1) K0 values and the maximum allowable sliding speed of SUN and PN products are set by KHK. Screw gears are typically used with lubrication. In case of using PN products without lubrication, the parenthetical values shown in the table are applied.

In order to use KHK stock screw gears safely, read the Application Hints carefully before proceeding. Also, please refer to the "Application Hints" in the technical information section on KHK stock spur gears, when performing secondary operations.
1. Points of Caution in Assembling
KHK stock screw gears are designed to give the proper backlash when assembled using the center distance given by the formula below with a tolerance of H7 to H8. The amount of backlash is given in the product table for each gear.

(Caution) PN Plastic Screw Gears are excluded.
Due to their helix, screw gears produce axial thrust forces. The bearings must be selected properly to be able to handle these thrust forces. The directions of thrust change with the hand of helix and the direction os rotation as illustrated below.
Direction of Rotation and Thrust Force
