Guides / Industries

Swiss Machining for RF and High Frequency Connectors

September 21, 2026

RF connectors look like ordinary turned metal parts and behave like precision instruments. A connector body carries a defined characteristic impedance along its length, and small geometric errors that would be irrelevant on a mechanical fitting become signal loss and reflection on an RF part. Swiss-type lathes make the small, concentric, feature rich bodies these connectors need, but the drawing has to carry information a mechanical part drawing does not.

The parts

Common Swiss RF and high frequency work:

Connector bodies. SMA, N-type, BNC, TNC and similar coaxial connector shells and center pins, machined from brass, beryllium copper or stainless depending on the frequency, environment and cost target.

Center contacts and pins. Slender turned pins that carry the signal conductor, often plated and held to tight concentricity against the body’s mating diameter.

Cable connector components. Crimp or solder bodies, ferrules and strain relief parts that make up the back end of a connector assembly.

Adapter and attenuator housings. Small precision bodies for RF adapters, attenuators and terminations, where internal geometry affects performance as much as the outer mating dimensions.

Antenna and feed components. Small turned parts for antenna feeds and connector to board transitions in RF and microwave assemblies.

Why concentricity is the real specification

A coaxial connector’s impedance depends on the ratio between the center conductor diameter and the inner diameter of the outer conductor, along with the dielectric between them. That relationship has to hold consistently along the connector’s length and stay coaxial, meaning the center conductor and the outer body share the same axis.

A Swiss-type lathe cuts a connector body’s features in one chucking, which is exactly what makes tight concentricity between diameters achievable without a second setup. The pillar guide covers why single chucking work holds concentricity well in general, and on an RF part that general advantage becomes the specification that matters most.

What belongs on the drawing:

• Concentricity between the center pin bore or the center conductor mating diameter and the outer body, stated as a value rather than left to a general tolerance block
• Any feature machined on the sub spindle that must stay concentric with the front, since front to back concentricity depends on how cleanly the sub spindle picks up the part, covered in the tolerances guide
• The critical diameters that set impedance, dimensioned with limits rather than a nominal alone

Plating for RF performance, not just protection

Plating on an RF connector does two jobs at once: it protects the base metal and it carries the signal current, because at radio frequency the current flows mostly in a thin layer near the surface rather than through the full cross section of the conductor. This is called skin effect, and it means the plating’s conductivity and surface condition matter for electrical performance in a way they do not on a purely mechanical part.

Common choices: silver plating for the best conductivity at a moderate cost, gold over nickel for corrosion resistance with acceptable conductivity, and tin for lower cost connectors where performance requirements allow it.

State on the drawing:

• The plating metal and thickness, tied to the frequency range and performance the connector needs to meet, not a generic connector standard
• Whether dimensions apply before or after plating, the same rule that applies to any plated part, covered in the secondary operations guide
• Surface finish under the plating where it affects signal loss, since a rough substrate telegraphs through a thin plating layer

Material choice

Brass is common for connector bodies where cost matters and the frequency range and environment allow it. It machines well and plates reliably. The brass guide covers the grades.

Beryllium copper appears in spring contacts and center pins where the part needs both good conductivity and mechanical spring properties, at a higher material cost than brass.

Stainless steel is used for connector bodies that need corrosion resistance or mechanical durability beyond what brass offers, at some cost to machinability and sometimes to conductivity if the stainless itself carries current rather than only the plating.

Tell the shop the frequency range and the environment, not just a material name. A connector rated for a harsh outdoor environment at a given frequency has different material and plating needs than an indoor board level connector, and the machining and finishing choices follow from that.

Testing and specification standards

RF connectors are frequently built to a defined standard, such as a MIL-DTL specification for a connector series, or a customer’s own performance specification covering insertion loss, return loss and mechanical mating cycle life.

If your part must meet a published connector standard, name it explicitly rather than relying on the shop to infer the requirement from a generic drawing. Some standards specify dimensions the shop can machine to directly. Others specify performance that depends on the assembly as a whole, in which case the machined part is one contributor among several and the shop needs to know which dimensions on the drawing are the ones actually controlling that performance.

What to send with an RF connector RFQ

1. STEP file and drawing, with impedance-critical concentricity and diameters identified
2. Material and plating specification tied to frequency and environment
3. Any connector standard the part must meet
4. Whether dimensions apply before or after plating
5. Testing requirements, if the shop is expected to verify electrical performance rather than only dimensional conformance
6. Yearly volume and expected order pattern

Common connector series and their dimensional standards

Several widely used RF connector series carry their own published mechanical interface standards, and naming the series on your drawing, alongside your own dimensional callouts, gives a shop a useful cross check against a recognized reference rather than relying solely on your drawing to be complete.

SMA connectors are common in the lower microwave frequency range, widely used in test equipment, RF modules and antenna connections, with a threaded coupling mechanism that depends on precise thread and mating face geometry to maintain performance.

N-type connectors handle higher power and are common in infrastructure and base station equipment, larger than SMA with a more robust threaded coupling suited to outdoor and higher stress environments.

BNC connectors use a bayonet coupling rather than a thread, common in test equipment and video applications where quick connect and disconnect matters more than the highest frequency performance.

TNC connectors are essentially a threaded version of BNC, chosen where the bayonet coupling’s vibration resistance is not sufficient and a threaded connection is needed instead.

Where your part conforms to one of these established series, a shop building to both the published series standard and your specific drawing has two references that should agree, and a discrepancy between them is worth resolving before the first article rather than after, the same principle covered generally in the tolerances guide about stating datums and critical relationships explicitly.

Assembly and cable termination

A connector body rarely ships as a standalone part. It gets assembled with a cable, a dielectric insulator, and sometimes a separate center contact, and how the machined body interfaces with these other components affects both assembly yield and final electrical performance.

Crimp and solder interfaces. The back end of a connector body, where it attaches to a cable, typically needs a specific bore diameter and surface condition to accept a crimp ferrule reliably or to solder cleanly, distinct from the front end’s mating geometry. State both requirements separately rather than assuming a general tolerance covers both ends equally.

Dielectric fit. Where a machined center contact or body interfaces with a dielectric insulator, usually PTFE or a similar low loss material, the fit between the metal and dielectric parts affects both assembly and the connector’s electrical performance, since an inconsistent fit changes the effective dielectric constant along the connector’s length. Confirm this interface dimension with whoever supplies the dielectric component, not just with the machine shop.

Assembly sequence. If your connector is assembled by a separate party from the one machining the body, make sure both understand which dimensions are critical to that assembly step, since a machined part that meets every printed dimension can still assemble poorly if an unstated functional relationship, such as concentricity to the dielectric bore, was not carried through clearly.

Frequency range and material selection together

The frequency your connector needs to handle at low loss narrows the practical material and plating choices more than most other requirements on the part. A connector rated for a modest frequency range in a benign, indoor environment gives you room to choose brass with tin plating for cost reasons. A connector rated for a demanding high frequency range, or one that must perform reliably outdoors over years of temperature cycling, generally pushes toward beryllium copper contacts and silver or gold plating, where the added cost buys performance and durability the application genuinely needs. Confirm the actual frequency and environmental requirement with your RF engineer before defaulting to a premium material specification that the application may not require, the same discipline covered in the materials guide for any Swiss machined part.

Getting RF connector parts quoted

Send the package through the RFQ form. We match your part with up to three shops that run Swiss-type lathes and reply within 24 business hours.

For the broader question of plating specification and tolerance stack up on small contact parts, the connector pins guide covers ground this article does not repeat.

Frequently asked questions

Keep reading

• Valve Spools on Swiss Lathes: Fits, Roundness and Finish
• Watch and Clock Parts on Swiss Lathes: Pinions, Winding Stems and Screws