Industries we serve

Furniture & Knock-Down Hardware

High-volume finishing for furniture screws, connector bolts, cam fittings and decorative heads — where the specification is colour, coverage and cost per thousand rather than a property class.

Furniture hardware is the one sector on this list where almost nothing is specified as strength. The complaint that costs a supplier the account is never "it broke" — it is "this batch is a different blue from the last one", or a driver bit that will not seat in a recess, or a scratched head visible on a showroom piece. The parts are small, the volumes are large, the price is quoted per thousand, and the acceptance criterion is usually an approved sample rather than a number. That makes repeatability, coverage on the visible surface and honest colour control the whole job.

Typical specification bands in this sector

Typical specification bands in this sector
Property class	usually none — the drawing states appearance and driving torque
Hardness	case ~450–560 HV on case-hardened tapping and confirmat screws
Materials	S20C · SWCH carbon steel · S45C
Coating system	Zn + Cr3+ clear / blue / black · black oxide + oil · zinc phosphate
Coating thickness	5–12 µm Zn — visible heads specified as a RANGE, not a minimum
Salt spray (NSS)	24–96 h NSS (indoor service)
De-embrittlement bake	decided by hardness, not by size — case-hardened tapping screws get reviewed
Inspection methods	ISO 3497 · colour against an approved master sample · driving torque check

Furniture drawings usually carry no property class, and that is correct rather than an omission — the load case is a hand-driven screw into board. If a class does appear on your drawing, tell us, because it changes both the process and the price.

Standards commonly cited

ISO 4042 ISO 2081 ASTM B633 MIL-DTL-13924 ISO 9227 ISO 3497 All standards →

Steel grades commonly specified

S20C SWCH10B21 S45C All steel grades →

How fasteners actually fail here

1Colour drift from batch to batch

Trivalent passivates and black finishes shift with bath age, concentration, temperature and drag-in, and blue, clear and black all have a visible spread rather than a single shade. Your customer is not comparing the delivery to a colour chart; they are comparing it to the parts already fitted to furniture on a showroom floor. The only workable control is a dated master sample held by both parties, agreed on which faces are compared and under what light, and re-issued when it ages.

2Thin or missing coating in the recess and under the head

Barrel plating deposits according to current distribution, and a cross recess, a blind socket or the underside of a wide decorative head are low-current-density areas. A thickness reading taken on the shank is a true measurement of the wrong place. Where the head is the surface the customer sees, the drawing has to name it as the significant surface, otherwise everyone is measuring what is easy to reach.

3Handling damage on decorative heads

Parts tumble against each other in a barrel, and a scratch through the passivate on a visible head is a reject even when the coating passes every thickness check. This is a genuine trade-off, not a defect to be eliminated by inspection: gentler handling means smaller loads and a higher price per thousand. It has to be decided at quotation, because a decorative head quoted at bulk-barrel prices will be delivered at bulk-barrel appearance.

4Tapping and confirmat screws that strip or snap in the drive

Screws that cut their own thread into board or into a cast fitting are loaded in torsion during driving, not in tension in service. Too soft and the point rolls over or the screw twists; too hard and the head snaps off in an assembly line or in a customer's living room. What controls it is the case and core relationship on a case-hardened screw, so the specification that matters is a hardness and case condition plus a driving test — not a property class, which these screws do not have.

Defect guides that matter in this sector

Blistering of the zinc coatingBubbles and lifted coating on plated screws: trapped hydrogen, contaminated substrate, laps and seams, and pre-treatment faults — plus the adhesion tests and sections that identify which one.Poor phosphate adhesion — coating rubs off, paint liftsPhosphate that wipes off, coarse powdery crystals and paint peeling from a phosphated fastener: cleaning, activation, bath control and post-treatment causes, with the practical checks that identify each.White rust on zinc-plated partsWhite powdery zinc corrosion in storage and transit: passivation, drying, sealer and packaging faults that cause it, and how to judge it against a salt-spray acceptance criterion.Low hardness after temperingBolts and screws that read under the drawing hardness: measurement error, temper temperature, hardenability limits and quench faults, ranked by how often each is the real cause.

All defect guides →

Documentation a buyer in this sector should receive

A dated approved master sample retained by both parties, with a written note of what it governs — colour, gloss, and which faces are compared. A sample with no agreement attached becomes an argument later.
Coating thickness measured on the named significant surface, with the method and the position, and reported against both limits so a heavy deposit in a recess is caught before assembly finds it.
Salt-spray testing only where the drawing genuinely calls for it. Indoor furniture hardware rarely needs long exposure, and hours bought on the report do not fix a colour complaint.
For a black oxide finish, a statement of what it actually is: a conversion coating of negligible thickness whose corrosion resistance comes almost entirely from the oil or wax applied after it. If the parts are handled by consumers or touch fabric, the oil type is part of the specification.
Lot traceability plus the agreed packing standard — bulk, counted bags or assembly kits. For small furniture hardware, packing is part of the reject rate, not an afterthought.
Every report carries job and lot identity, material and agreed specification, position, method and instrument, measured values against the limits, and date, inspector and approval, under ISO 9001:2015.

What to send us for an accurate quote

1The visible surface, named on the drawing or marked on a photo — the head face, the head and collar, or the whole part.
2Colour and finish with a physical sample or an agreed reference, and the lighting the comparison is made under.
3A thickness range with a maximum as well as a minimum, because a heavy deposit rounds a recess and stops the driver bit seating.
4Whether the screw is case-hardened and self-tapping, and any driving-torque or torsional requirement that applies.
5Zinc versus black oxide versus phosphate, and whether the part is handled by consumers or packed against fabric or paper.
6Monthly volume, packing format, piece weight and the price basis you are quoting to your own customer.

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Recommended services

Zinc Plating Cr3+Phosphate Coating Heat Treatment

Common parts we finish

Screws Nuts Bolts Washers Pins All part types →

Questions buyers in this sector ask

Can you match the black on our current supplier's screws?+

Send physical parts rather than a colour name. Black trivalent zinc and black oxide are different systems: one is a plated coating with a black passivate, the other a conversion coating that owes its appearance and its modest corrosion resistance to the oil on top. They do not look identical side by side and they do not age the same way. With samples in hand we will tell you which system yours is and whether we can hold it batch after batch.

Do furniture screws need heat treatment at all?+

Machine screws and connector bolts in knock-down fittings usually do not — they are loaded well below anything that needs a property class. Self-tapping, chipboard and confirmat screws are a different case: they are case-hardened so the point can cut and the shank can carry the driving torque without twisting. Tell us which of the two you have; quoting a plating job for the first and a heat-treatment plus plating job for the second are very different conversations.

How thick should the zinc be on a decorative head?+

Thick enough for the indoor service life and no thicker, which is why we ask for a range with a maximum. Zinc grows the effective pitch diameter by roughly four times the local thickness, and in a recess a heavy deposit rounds the drive geometry so the bit cams out during assembly. For indoor furniture the appearance and the fit usually set the upper limit long before corrosion sets the lower one.

The bands on this page are typical industry values, not a guarantee for any specific part. The governing drawing, customer specification and standard always take precedence, and every value is confirmed against your part before production. V.S. Heat Treatment operates under ISO 9001:2015; no other certification or sector approval is claimed.