C6635-4 Press-Fit Nut Specs Datasheet and Procurement Verification Guide
C6635-4The C6635-4 is a #2-56 threaded brass press-fit nut manufactured by Carlisle Interconnect Technologies, categorized under Nuts within Hardware, Fasteners, Accessories. This component provides a threaded insert for thin panels where conventional nut engagement is impossible. Procurement and quality teams must verify mechanical dimensions, thread fit, plating integrity, and lot traceability to avoid field failures in aerospace, medical, or industrial assemblies.
Visual and Marking Inspection Standards for C6635-4
Counterfeit or relabeled press-fit nuts typically fail at marking legibility or material appearance. The C6635-4 uses laser-etched marking for permanent identification. Verify the "Kwik" type designation and thread size "#2-56" are crisp, not blurred or painted. Ink markings or pad-printed characters indicate a relabeled or non-OEM part. Examine the plating: Nickel plating should have a uniform satin-to-bright finish without peeling, blistering, or copper bleed. Brass substrate exposure at corners or edges signals poor plating thickness or post-plating handling damage.
Decode the YYWW lot code laser-etched on the nut face. YY indicates manufacturing year, WW the work week. A code "2425" means year 2024, week 25. Nuts with codes older than five years from current date may have degraded nickel plating adhesion. Reject any part where the code is partially erased, over-stamped, or missing entirely. Document the lot code on your incoming inspection report for traceability to Carlisle Interconnect Technologies' certificate of conformance.
Critical Dimensional and Thread Verification Methods
Table 1 lists the supplier-must-confirm parameters for C6635-4 with pass/fail criteria. Use a calibrated digital caliper or micrometer (resolution 0.001 inch) for width and thickness. The 0.192" width (4.88 mm) is the hex or knurl diameter that interfaces with the press-fit hole. Measure across flats if hexagonal; measure the outer knurl diameter if round. Tolerance is typically ±0.003" for press-fit hardware, but consult the latest datasheet for this part.
Thread inspection requires a GO/NO-GO plug gauge for #2-56 UNC-2B. The GO gauge must advance fully through the nut without binding. The NO-GO gauge may enter up to three threads maximum. Reject if the nut accepts a #2-56 screw with visible play or if the NO-GO gauge passes more than 3 turns. For high-reliability applications, use a thread depth micrometer or optical comparator to confirm thread minor diameter (0.078" - 0.082" typical for #2-56). Undersized threads strip under torque; oversized threads cause loose fasteners.
| Parameter | Value | Engineering Meaning |
|---|---|---|
| Thread Size | #2-56 | Specifies the mating screw diameter (0.086" major diameter) and 56 threads per inch. Common in compact PCB mounting and panel fasteners. |
| Thickness | 0.167" (4.24 mm) | This parameter indicates the height of the nut after installation. Affects thread engagement length — minimum 2 full threads needed for load capacity. |
| Width | 0.192" (4.88 mm) | Outer diameter of the press-fit feature. Determines the required hole size in the panel or PCB. Values above this level usually cause cracking in brittle substrates. |
| Material | Brass | Brass offers good corrosion resistance and machinability. Not suitable for high-temperature (>250°C) or high-vibration environments without plating. |
| Plating | Nickel | Nickel provides corrosion protection and improves solderability if secondary soldering is required. Typical plating thickness ranges from 0.0002" to 0.0005". |
| Type | Kwik | Specialty parameter — see datasheet. Likely refers to a quick-install press-fit design with optional anti-rotation knurling. |
| RoHS | Compliant | — |
Two parameters warrant deeper analysis. Thickness at 0.167" combined with #2-56 thread provides roughly 2.5 threads of engagement when installed flush with a 0.062" PCB. This is acceptable for static loads but marginal for frequent assembly/disassembly cycles. For applications requiring higher pull-out resistance, specify a thicker nut from the same family or add thread-locking compound. Width at 0.192" implies a press-fit hole diameter between 0.185" and 0.190" in FR4 or aluminum. Exceeding the maximum recomended hole diameter reduces retention force; using a smaller hole may crack the panel. Always verify the PCB or chassis manufacturer's drilled hole tolerance against this width.
X-Ray and Destructive Analysis for High-Value C6635-4 Batches
For orders above 500 units or applications in flight-critical assemblies, perform X-ray inspection on a sample of five pieces per lot. X-ray reveals internal voids in the brass blank, incomplete knurling depth, or cracks from improper pressing that could cause the nut to spin during torque application. Set X-ray parameters at 50-70 kV with 100 ms exposure. Reject any part showing porosity exceeding 10% of the nut body cross-section or any crack longer than 0.010".
Destructive decapsulation (cross-sectioning) should be performed only when counterfeit is suspected or when plating thickness certification is absent. Mount the nut in epoxy, grind to the center axis, and etch with ferric chloride. Measure nickel plating thickness at three points — minimum acceptable is 0.0002". Brass grain structure should show equiaxed grains, not elongated, which suggests cold-forming without proper annealing. Decap data must be recorded and compared against a known-good sample from Carlisle Interconnect Technologies.
Packaging, Labeling, and Certificate of Conformance Checks
Carlisle Interconnect Technologies ships C6635-4 in anti-static polybags or tape-and-reel reels with a sealed ESD bag. Verify the label includes: part number C6635-4, lot number, quantity, and RoHS compliance marking. A missing manufacturer address or blurred barcode is a red flag. Open the bag and check for debris, discoloration, or oil residue. Press-fit nuts must be dry and free of machining lubricant to ensure proper press-in retention.
Request a Certificate of Conformance (CoC) from your distributor. The CoC must state the manufacturer name, part number, lot number, and date of manufacture. Cross-check the lot number on the CoC with the lot code etched on the nuts. Discrepancy in lot numbers between CoC and physical parts indicates mixed lots or possible counterfeits. For RoHS compliance, the CoC should reference IPC 1752 or similar declaration. A supplier unable to provide a CoC within 24 hours should trigger an automatic quality hold on the shipment.
AQL Sampling Plan with Accept/Reject Criteria
Use AQL (Acceptable Quality Level) sampling per ANSI/ASQ Z1.4, normal inspection level II. For a lot of 1000 C6635-4 units, sample 50 pieces. Major defects (thread failure, wrong material, missing plating) have AQL 0.65% → accept 0, reject 1. Minor defects (marking legibility, slight burr <0.003") have AQL 2.5% → accept 3, reject 4. Critical defects (lot code mismatch, counterfeit indicators) require zero-tolerance — any single critical defect rejects the entire lot. Perform dimensional inspection on the first 10 sample units; if all pass, reduce to 5 units for remaining lots in the same order. Record results on an incoming inspection checklist with the test instrument calibration date.
Frequently Asked Questions About C6635-4
What is the recommended hole size for the C6635-4 press-fit nut?
The C6635-4 width is 0.192" (4.88 mm). For a standard press fit, drill the mounting hole between 0.185" and 0.190" in FR4 or aluminum. Always test the fit on a sample piece before full production, as material hardness varies. A hole smaller than 0.185" may crack the panel; larger than 0.190" reduces retention force.
Is the C6635-4 RoHS compliant and lead-free?
Yes, the C6635-4 is marked RoHS compliant. The nickel plating process does not add lead, and the brass substrate typically contains less than 1000 ppm lead. Request a RoHS declaration of conformity from the distributor for your compliance records.
How can I verify the C6635-4 is not counterfeit?
Check three things: laser-etched marking must be permanent and include a YYWW lot code, the nickel plating must not show copper bleed at edges, and the thread must pass a #2-56 GO gauge. For high-value orders, request a Certificate of Conformance from Carlisle Interconnect Technologies and perform X-ray on a small sample to detect internal voids.
Procurement workflow summary. For C6635-4, prioritize marking verification and thread gauging during incoming inspection. Lot code traceability is essential — store nuts in original ESD bags with CoC. For critical aerospace or medical builds, add X-ray sampling and torque testing (0.5 in-lb min pull-out). Share these verification criteria with your supplier upfront to reduce rejection rates. This press-fit nut is mechanically straightforward but demands dimensional discipline at the PCB or chassis fabrication stage.
