Use screws or bolts according to the flange drawing, access and required clamp load; screws do not inherently produce lower RF leakage. A tapped flange and a through-hole flange need different fastening arrangements. Specify thread, engagement, material, finish and tightening procedure together, and verify the assembled joint against its RF and sealing requirements.
What determines whether a screw or bolt fits the joint?
The flange hole arrangement and available access determine the practical fastening method.
A machine screw may engage a tapped flange; a through fastener may use a nut on the opposite side. Check head clearance, driver access, washer requirements and whether the tip could bottom out or enter the RF opening. Terminology alone is not a design specification.
Use the drawing for the selected EIA or IEC waveguide flange to identify the actual thread and mating features. Do not infer a screw thread from a WR number alone.
Why is torque not a universal RF setting?
Torque is a means of producing preload, and the relationship depends on the joint and friction conditions. NASA’s Fastener Design Manual covers material, plating, lubrication, locking methods and torque as related design choices.[1]
The same torque can produce different preload after a change in lubrication or finish. Use the approved assembly value and condition; do not transplant a torque from another flange size or material. A screw bottoming in a blind hole may indicate tightening without clamping the mating faces.
| Check | Possible error | Action before assembly |
|---|---|---|
| Thread and pitch | Near-fitting thread forced into flange | Verify designation and gauge if required |
| Engagement and depth | Bottoming or insufficient engagement | Check usable hole depth and stack-up |
| Material and finish | Galling or incompatible friction assumptions | Match approved hardware specification |
| Access and head style | Incomplete tightening or damaged recess | Confirm installation-tool clearance |
| Seal and mating face | Uneven compression or trapped debris | Inspect joint and follow assembly procedure |
How does fastening affect RF performance?
Fastening affects the alignment and contact condition of the assembled interface; it does not assign a fixed leakage reduction by fastener type.
Clean faces, suitable locating features and controlled clamping can be more relevant than whether a catalogue calls the hardware a screw or bolt. If a joint is sealed, the gasket or O-ring needs its specified groove and compression arrangement. Do not add washers, sealants or shims as an improvised RF correction.
What should be recorded after a fastener change?
Record the approved hardware and tightening procedure, then perform the checks required for the affected joint.
Include part number, thread, length, finish and any locking or reuse restriction. Compare RF performance before and after remating under the same setup. For a pressurized assembly, complete the specified leak check separately; a good RF match does not prove pressure integrity.
Table of Contents
Do screws reduce leakage more than bolts?
There is no universal percentage advantage. RF behavior depends on the flange geometry, alignment, contact and operating frequency. Select hardware that produces the required joint condition, then verify the assembly using the project’s RF and sealing acceptance requirements.
Can stainless steel replace every original fastener?
No. Check strength, corrosion compatibility, finish, friction and locking requirements first. A substitution can change preload at the same torque or introduce galling. Use the approved hardware specification or obtain an engineering assessment before making a material change.
Is hand tightening sufficient for a waveguide flange?
Use the equipment’s specified assembly procedure. Hand feel does not establish a repeatable clamp load, and excessive tightening can damage threads or mating parts. Confirm the correct hardware, tool and tightening condition rather than applying a generic torque figure.
Send the flange drawing, hole/thread details, existing fastener specification and installation clearance for a mechanical-interface review.
