Height of an extension spring hook
 
where:
| L 0 | length of free spring [mm] | 
| L Z | length of spring coiled part [mm] | 
Most frequently used hooks of extension springs
| Hook type and dimension instructions | Image | 
| Half hook, o = 0.55 to 0.8 D 2 | 
 | 
| Usually: d ≤ 6.3 mm, D >= 3.15 mm, i >= 9 | |
| Full loop, o = 0.8 to 1.1 D 2 | 
 | 
| Used generally | |
| Full loop on side, o ≈ D 2 | 
 | 
| When moving the force out of spring axis does not matter | |
| Full loop inside, o = 1.05 to 1.2 D 2 | 
 | 
| Usually: d ≤= 10 mm, i >= 7 | |
| Raised hook, o = 1.2 D 2 to 30 d | 
 | 
| Usually for: d = 0.5mm to 4 mm, o ≤ 100 mm | |
| Double twisted full loop, o ≈ D | 
 | 
| Used generally | |
| Double twisted full loop on side, o ≈ D 2 | 
 | 
| When moving the force out of spring axis does not matter | |