Fasteners 101: Bolts, Nuts & Washers

Fasteners look like the simplest product in a hardware catalog — until you try to order them. Metric or SAE? Grade 8.8 or 12.9? Zinc plated or hot-dip galvanized? The wrong choice leaves you with stock that nobody buys, while the right assortment turns fasteners into a steady, high-repeat business: customers who buy bolts come back for nuts, washers, anchors, and everything else.

This guide covers the essentials every fastener buyer should know.

Metric vs. SAE (Imperial)

Two measurement systems, two markets:

• Metric (M6, M8, M10, M12…) — used almost everywhere except the United States. Bolt diameter is the “M” number in millimeters; length is measured in millimeters from under the head.
• SAE / Imperial (1/4", 5/16", 3/8"…) — standard in the US market, and common in older machinery worldwide.

Wholesale tip: If your market is anywhere outside North America, lead with metric. Popular retail ranges are M5–M12 in lengths from 16 mm to 120 mm. For the US market, 1/4"–1/2" is the fast-moving range.

Understanding Strength Grades

Bolt grade markings tell you tensile strength — and price:

Metric bolts (property class):

SAE bolts (grade lines on the head): Grade 2 (no marks) = general purpose; Grade 5 (3 marks) = automotive/machinery; Grade 8 (6 marks) = high strength.

Rule of thumb for assortment buying: 8.8 is the sweet spot for most markets — strong enough for serious work, affordable enough for retail pricing. Nuts should match or exceed the bolt class.

Washers: The Small Part That Matters

• Flat washers — spread the load and protect the surface. The default in any assortment.
• Fender washers — extra-wide bearing surface for soft materials (plastic, wood, thin sheet).
• Spring lock washers (split) — resist loosening from vibration.
• Tooth lock washers — stronger vibration resistance; used in electrical and automotive assemblies.
• Nylon insert lock nuts — the most reliable anti-loosening option; pairs with any bolt in the assortment.

Surface Finishes and Corrosion Protection

Finish affects both appearance and how the fastener survives your customer’s climate:

• Zinc plated (blue-white or yellow) — the default export finish; good indoor and light outdoor protection at minimal cost.
• Hot-dip galvanized (HDG) — thick coating for outdoor, coastal and marine use. Essential for construction-market assortments.
• Black oxide — decorative, mild protection; popular for furniture and interior hardware.
• Dacromet / geometric coating — salt-spray resistance of 500–1000+ hours; specify for automotive and harsh-environment buyers.

Climate tip: For humid coastal markets (Southeast Asia, island nations, coastal Latin America), upgrade zinc plating thickness or offer an HDG line — it is a genuine selling point against cheap competitors.

Building an Assortment That Sells

The fastest-moving retail format is the boxed or blister-packed assortment: one SKU covering a range of sizes. Proven configurations:

1. Hex bolt & nut kits — M5/M6/M8 with matching nuts and washers, 100–300 pieces
2. Washer sets — flat + lock washers in a divided box
3. Furniture bolt kits — with barrel nuts and dowel screws for flat-pack furniture repair
4. Anchor assortments — expansion anchors with matching screws (always include the screw!)

Quality Checks Before You Commit

• Thread check: a matching nut should run the full thread length smoothly by hand
• Head stamping: grade markings crisp and legible (fake grade marks are common in low-end supply)
• Coating uniformity: no bare spots on thread crests
• Sample salt-spray test if your market is coastal — ask the supplier for test reports

Related Products

Browse our wholesale catalog: Bolts & Nuts, Washers & Rings, Rivets & Pins and Anchors.

Want a mixed fastener assortment quote? Send us your size list on WhatsApp — as a Yiwu-based wholesaler we consolidate multiple fastener lines into one low-MOQ shipment.