Each circle is formed into a tightly closed spiral ring or a pitch ring, which extends outwards when subjected to external forces and maintains a force of contraction towards the middle.
There are many kinds of spring hooks: English hook, German hook, earring hook, fishtail hook, etc.
(1) free length: (a) total length, (b) total length of the ring, and (c) length inside the hook ring.
(2) control diameter :(a) outside diameter, (b) inside diameter, (c) inside diameter of casing.
(3) steel wire size "wire diameter".
(4) materials (type, grade).
(5) winding number :(a) total winding number and (b) right or left turn.
(6) terminal form.
(7) load in the hook.
(8) load rate, deflection, weight per inch.
(9) maximum stretching length.
The Extension Spring is a typical Spring, which can be shaped by design from straight to various variants, or even the shape of the hook.
The Extension Spring is the reverse operation of the compression Spring. The application range is generally less than the product category, but the operation control is higher than the compression Spring.