Resource
Torsion vs extension vs compression springs
The assembly either pushes, pulls or twists. Pick the spring that does that one thing. The drawing still has to give wire, size and load.
Which motion?
If the part shortens and must push back, you want a compression spring — or a conical spring when solid height has to be very short.
If the part lengthens and must pull back, you want a tension / extension spring. Specify the hooks.
If the part rotates around a pin, you want a torsion spring. If both sides of a hinge must push together, that is usually a double torsion spring.
Compression
Open-coiled. Rate k = G · d⁴ / (8 · D³ · Na). Watch solid height and buckling (free length more than about four times the mean diameter). Ends: open, closed, or closed and ground.
Extension
Close-wound. The body does not start to open until the pull beats initial tension. The hook is bent tighter than the body, so it usually fails first. See end types.
Torsion and double torsion
Legs rotate around the coil. Wind direction must match the load or the spring unwinds the wrong way. A double torsion spring joins two opposite-wound coils with a centre loop so the hinge sees balanced torque. That is the largest share of what leaves our unit.
Clips, hooks and pins that are not a helix are wire forms.