Structure: Spring contact probes

The basic body of spring contact probes always consists of a plunger, barrel and spring. Due to the spring, the contact probe can perform a defined working travel and also compensate for tolerances. Depending on the type of probe, further functions can be installed (e.g. thread, insulation, switching functions, etc.).


FEINMETALL manufactures plungers with a variety of tip styles for a wide range of contacting tasks. Copper beryllium (BeCu) or steel are used as the base material. The plungers are turned with the utmost care to achieve a high degree of straightness and a slippery surface. Aggressive tip styles with sharp edges are produced in a special grinding process.

Plunger: Base material and coating


Base material

  • Copper-Beryllium - BeCu (B)
  • Steel (S)
  • Synthetics (K)
  • Palladium alloy (P)
  • Brass (M)


  • Chemical nickel
  • Gold
  • FM-Longtime gold
  • Rhodium
  • Progressive Coating Multiplex


FEINMETALL barrels are normally made of nickel silver, bronze or brass. Nickel silver barrels are deep-drawn. Bronze barrels are turned or deep-drawn and are characterized by a particularly long service life. Brass barrels are turned. All barrels are generally plated with silver or gold. A small opening on the underside allows thorough cleaning during production and ensures continuous wetting during the coating process.

Barrel: Base material and coating


Base material

  • Nickel silver (deep drawn)
  • Bronze (turned or deep drawn)
  • Brass (turned)
  • Nickel


  • Gold
  • Silver


FEINMETALL manufactured long-life springs for the watch industry at a very early stage and applied this knowledge to the production of spring contact probes. Contact probes usually have cylindrical springs with a linear force-travel characteristic. The springs are made of silver-plated or gold-plated spring steel, stainless steel or, in special cases, non-magnetic BeCu. Springs made of spring steel can be used up to a working temperature of + 80°C, springs made of stainless steel and CuBe up to + 200°C.

Spring: Base material and coating


Base material

  • Spring steel (max. 80°C)
  • Stainless steel (max. 200°C)
  • BeCu (non-magnetic, max. 200°C)


  • Silver
  • Gold

Spring force

The spring force is matched to the application of the probe. It should always be selected to ensure reliable contacting and good penetration of contaminants on the contact surface, but without causing damage. With the same spring force, the contact area of the tip style determines how strongly the contact point is penetrated. In the case of test fixtures, especially vacuum fixtures, the sum of the spring contact probes always consists of a plunger, barrel and spring as the basic body. The spring forces of all contact probes used must be observed to ensure trouble-free closing and contacting of the fixture.

A tolerance of ±20% of the spring force must be observed due to deviations in the basic spring material and manufacturing tolerances.

Spring travel (stroke)

The spring force of a contact probe increases proportionally to the spring travel. This dependence is shown in a so-called force-travel diagram. When the spring contact probe is fully assembled, the spring is usually compressed by a defined travel. The resulting spring force is called preload. It ensures a specific force effect right at the start of the contacting travel and ensures that the plunger returns back completely after contacting. When the recommended spring travel (nominal travel) is reached, the nominal spring force is achieved.

In practical use, the recommended spring travel (nominal travel) should not be significantly exceeded, otherwise the life time of the spring may be significantly reduced.

Graphic: Force-travel diagram

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