Copper is bought for conductivity — electrical and thermal — and almost every distinction between the seven grades here is a trade of conductivity against something else. Six of them are coppers at 99.9% purity or better, and they differ only in how the residual oxygen is dealt with and whether a machining addition is present; the seventh, C19400, is a copper-iron alloy that trades conductivity for strength. The oxygen question matters more than it sounds: tough-pitch C11000 carries its oxygen as cuprous oxide and embrittles if heated in hydrogen, which is why the oxygen-free grades C10100 and C10200 and the phosphorus-deoxidised grades C12000 and C12200 exist at all. Exotic Alloy manufactures copper fasteners to ASTM F468 and F467 for nonferrous bolts and nuts, with full EN 10204 3.1 certification.
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This is the most common specification error in the family, so it is worth stating plainly. Even at hard temper a copper bolt develops roughly 330–380 MPa tensile, against 830 MPa for an ordinary ASTM A325 structural bolt and 1040 MPa for a property class 10.9. Copper is specified when the fastener has to carry current, conduct heat, resist a corrosive environment, stay non-magnetic or avoid sparking — and the structural duty is light or carried by something else. Where a copper-base fastener is wanted at real strength the answer is a copper alloy — silicon bronze, aluminium bronze or beryllium copper — not one of the high-conductivity coppers here.
Stress relaxation is the companion problem. Copper creeps at modest temperature under sustained load, so a bolted copper joint loses preload over time — faster when soft-tempered and faster when warm. Copper electrical connections must therefore either be re-torqued on a schedule, or use a spring element such as a Belleville washer to take up the relaxation, or use C19400, whose iron-phosphide dispersion gives far better relaxation resistance than any pure copper. A copper busbar bolt torqued once and forgotten becomes a loose, hot joint later.
Hydrogen embrittlement rules out tough-pitch copper for welded and furnace-brazed work. C11000 contains its residual oxygen as cuprous oxide; heated above roughly 400 °C in a reducing atmosphere, diffusing hydrogen reduces those particles in situ and the resulting steam opens intergranular cracks. The damage is permanent and invisible from the surface — ASTM B577 exists specifically to test for it. C11000 must not be oxyacetylene welded or brazed in a hydrogen furnace. Specify C10200, C12000 or C12200 at the design stage instead.
Ammonia and amines crack copper under stress. A tightened copper bolt carries exactly the sustained tensile stress that stress-corrosion cracking needs, and moist ammonia, ammonium compounds, the amine inhibitors used in boiler and condensate systems, nitrites and mercury compounds will all crack it without warning. Copper fasteners should not be used in ammonia refrigeration plant, fertiliser service, amine-treated condensate systems, or anywhere decaying organic matter concentrates ammonia.
Copper is galvanically noble, so it damages what it is bolted into. It sits well above carbon steel, cast iron, aluminium, zinc and galvanised coatings on the galvanic series. A copper fastener in an aluminium or galvanised assembly will survive while driving rapid corrosion of the surrounding metal, which is why aluminium-to-copper electrical connections use bimetallic lugs rather than a direct bolted lap. Isolate copper from aluminium and galvanised steel with insulating washers and sleeves or a barrier coating. Copper is compatible with the other coppers and bronzes, with the copper-nickels and with Monel.
Copper machines badly, and that governs how copper fasteners are made. On the CDA scale, where free-cutting brass C36000 is 100, the high-conductivity coppers rate 20 — copper is soft, extremely ductile and tough, so it does not break a chip but produces long gummy swarf that wraps the tool, smears into built-up edge and tears rather than shears. The answer is to form rather than cut: capacity for cold working and hot forming are both rated Excellent and the forgeability rating is 65, so copper cold heads, upsets, rolls threads, spins and deep draws better than almost any other engineering metal. Exotic Alloy forms copper fasteners wherever the geometry allows, and where significant machining is unavoidable we change grade rather than fight the material — C14500 tellurium copper machines at a rating of 85 while still retaining 93% IACS.
Conductivity, composition and property data from the Copper Development Association alloy records. UTS range spans annealed to hardest standard temper.
| Grade | EN / CEN | Cu min | Key Addition | Conductivity | UTS Range | Machinability | Chosen For |
|---|---|---|---|---|---|---|---|
| C10100 | Cu-OFE / CW009A | 99.99% | None — vacuum cast, O ≤ 5 ppm | 101% IACS min | 221–393 MPa | 20 | Electronic purity, vacuum service |
| C10200 | Cu-OF / CW008A | 99.95% | None — oxygen-free, O ≤ 10 ppm | 100% IACS min | 221–393 MPa | 20 | Hydrogen immunity at lower cost |
| C11000 | Cu-ETP / CW004A | 99.90% | None — tough pitch, residual Cu₂O | 100% IACS min | 221–393 MPa | 20 | General electrical; ASTM F468/F467 bolts |
| C12000 | Cu-DLP / CW023A | 99.90% | 0.004–0.012% P | 98% IACS | 221–393 MPa | 20 | Weldable with near-full conductivity |
| C12200 | Cu-DHP / CW024A | 99.9% | 0.015–0.040% P | 85% IACS | 221–393 MPa | 20 | Best weldability; plumbing and HVAC |
| C14500 | CuTeP / CW118C | 99.90% | 0.40–0.7% Te, 0.004–0.012% P | 93% IACS | 221–386 MPa | 85 | Machined and turned copper parts |
| C19400 | CuFe2P / CW107C | 97.0% | 2.1–2.6% Fe, 0.015–0.15% P | 65% IACS | 310–552 MPa | 20 | Strength and stress-relaxation resistance |
Copper strength comes from temper, not heat treatment — none of these grades is hardenable by heat treatment, and the temper designation is the most important item on the order after the UNS number. The sequence runs O60 or the OS grain-size tempers (annealed), then H00, H01, H02, H04, H06, H08 and H10, with tensile strength roughly doubling and elongation falling from 45–50% to around 4% across that range. Of the seven grades, only C11000 is listed by ASTM F468 and F467 for nonferrous bolts, screws, studs and nuts; the others are supplied to the composition and temper requirements of their own product standards. Werkstoff numbers are not consistently assigned to Cu-OFE or CuFe2P across published cross-reference tables, so those two should be ordered against the EN or UNS designation rather than a material number.
We are committed to delivering zero-defect copper fasteners. All products undergo rigorous testing including PMI (Positive Material Identification), electrical conductivity testing to ASTM B193, temper and grain-size verification, ASTM B577 hydrogen-embrittlement testing on tough-pitch material, dimensional inspection and full traceability with EN 10204 3.1 certification.
Exotic Alloy exports copper fasteners and electrical hardware to power transmission, switchgear, electronics, plumbing, HVAC and heat exchanger clients worldwide. Our dedicated logistics team ensures secure export packaging and timely deliveries by sea and air freight with full customs documentation support.