German Hook Spring

Description of parameters for extension springs with German hooks
Physical parameters

d (wire diameter): This parameter describes the diameter of wire used as material for spring.
De (external diameter): External diameter of a spring concerns both hooks and coils. Tolerance for this parameter is (+-)2%(indicative).
H (Hole): This is minimum diameter of hole in which spring can work. Tolerance for this parameter is (+-)2%(indicative).
Ln (Maximum length): Maximum acceptable extension length for a spring. It is also the maximum extension for static applications. Tolerance for this parameter is (+-)15%(indicative).
Fn (Maximal force): Maximal acceptable force which can operate on a spring. It is also the maximum force for static applications. Tolerance for this parameter is (+-)15%(indicative).
L0 (free length): Free length is measured in spring's free state. Tolerance for this parameter is (+-)2%(indicative).
Nr of coils: This is a total number of coils in a spring - in the picture above it is equal to six.
R (Spring rate): This parameter determines spring's resistance, while it is working. It is measured in 1 DaN/mm = 10 N/mm. Tolerance for this parameter is (+-)15%(indicative).
L1 & F1 (length under charge F): The charge F1 at length L1 can be calculated using the equation : F1 = Fn - R(Ln-L1). Equation derived from the previous for calculating L1 = Ln - (Fn-F1)/R.
Hooks: Extension springs with german hooks are produced in two versions: with hook positions of 0 degrees and 90 degrees as shown in the picture above.
Reference Number: All springs are identified by a unique reference: type . (De * 10) . (d * 100) . (L0 * 10) . material . [X if hooks are perpendicular to each other] ; for german extension springs, type is a letter "U", materials are identified by the following letters: "A" or "I". Example: U.063.090.0100.AX is an extension spring with an external diameter of 6.3 mm and a free length 10mm, produced from 0.9mm music wire with perpendicular hooks.