| Parallel Helical Gear | Crossed Helical Gear |
|---|
| Parallel helical gears can transmit motion and power between parallel shafts only. | Crossed helical gears can transmit motion and power between perpendicular but not-intersecting shafts. |
| Two mating gears must be mounted on two parallel shafts. | Two mating gears are mounted on two perpendicular but non-intersecting shafts. |
| Two mating gears should have same helix angle but opposite hand of helix. | Two mating gears may have different helix angles. They may have either same or opposite hand of helix. |
| Engagement between two teeth starts with a point contact but gradually becomes a line contact. | Two meshing teeth always have point contact. |
| Power transmission capacity of parallel helical gear is higher due to broader contact. | Crossed helical gear has lower power transmission capacity due to point contact. |
| It has wide area of application ranging from small equipment to large industrial field including gear trains. | It is rarely used in small size instruments. |
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