SAE Flat Washers (Inch Series)
SAE-pattern flat washers for inch hardware — the narrow-body series from #4 through 2" nominal size, with a smaller outside diameter and thinner section than USS at the same bolt size to fit tighter clearances around the fastener. Dimensioned per ASME B18.21.1 plain-washer tables.
Last updated: 2026-11
Specifications
SAE (Society of Automotive Engineers) is the compact flat washer of the inch series. Where the USS pattern widens and thickens to spread load, the SAE pattern keeps a smaller outside diameter and a lighter section — a 1/4" SAE washer runs about 0.625 in OD at 0.051–0.080 in thick — so it fits where clearance around the fastener is tight. It is the compact counterpart of the wide USS body, and the smallest sizes carry numbered designations (#4 through #12) for the numbered-series screws they accompany; fractional sizes continue up to 2". Inside-diameter, outside-diameter and thickness tolerances are tabulated per size. Like the USS series, SAE washers are commonly stocked plain, zinc-plated, in stainless steel, or in brass.
| Standard | ASME B18.21.1, inch-series plain washers (legacy SAE series; older references cite ASME B18.22.1) |
|---|---|
| Size range | #4 – 2" nominal size (numbered sizes #4–#12, fractional 1/4"–2") |
| Dimensions at 1/4" | ID 0.281 in × OD 0.625 in × 0.051–0.080 in thick |
| Tolerances | ID/OD +0.008 to +0.045 plus / −0.005 to −0.010 minus by size; thickness min–max per size step |
| OD character | Narrower and thinner than USS at the same bolt size — fits tighter clearances around the fastener |
| Materials and finishes | Plain steel, zinc-plated steel, stainless steel, brass (common trade stocking range) |
| Typical use | Inch-series hardware where clearance around the fastener is tight; compact fit is the pattern's purpose |
| Metric counterpart | DIN 125 / ISO 7089 regular-series flat washers |
| Nominal size | ID basic (in) | ID tol + | ID tol - | OD basic (in) | OD tol + | OD tol - | TH max (in) | TH min (in) |
|---|---|---|---|---|---|---|---|---|
| #4 | 0.125 | 0.008 | 0.005 | 0.312 | 0.008 | 0.005 | 0.040 | 0.025 |
| #6 | 0.156 | 0.008 | 0.005 | 0.375 | 0.015 | 0.005 | 0.065 | 0.036 |
| #8 | 0.188 | 0.008 | 0.005 | 0.438 | 0.015 | 0.005 | 0.065 | 0.036 |
| #10 | 0.219 | 0.008 | 0.005 | 0.500 | 0.015 | 0.005 | 0.065 | 0.036 |
| #12 | 0.250 | 0.015 | 0.005 | 0.562 | 0.015 | 0.005 | 0.080 | 0.051 |
| 1/4 | 0.281 | 0.015 | 0.005 | 0.625 | 0.015 | 0.005 | 0.080 | 0.051 |
| 5/16 | 0.344 | 0.015 | 0.005 | 0.688 | 0.015 | 0.007 | 0.080 | 0.051 |
| 3/8 | 0.406 | 0.015 | 0.005 | 0.812 | 0.015 | 0.007 | 0.080 | 0.051 |
| 7/16 | 0.469 | 0.015 | 0.005 | 0.922 | 0.015 | 0.007 | 0.080 | 0.051 |
| 1/2 | 0.531 | 0.015 | 0.005 | 1.062 | 0.030 | 0.007 | 0.121 | 0.074 |
| 9/16 | 0.594 | 0.015 | 0.005 | 1.156 | 0.030 | 0.007 | 0.121 | 0.074 |
| 5/8 | 0.656 | 0.030 | 0.007 | 1.312 | 0.030 | 0.007 | 0.121 | 0.074 |
| 3/4 | 0.812 | 0.030 | 0.007 | 1.469 | 0.030 | 0.007 | 0.160 | 0.108 |
| 7/8 | 0.938 | 0.030 | 0.007 | 1.750 | 0.030 | 0.007 | 0.160 | 0.108 |
| 1 | 1.062 | 0.030 | 0.007 | 2.000 | 0.030 | 0.007 | 0.160 | 0.108 |
| 1 1/8 | 1.250 | 0.030 | 0.007 | 2.250 | 0.030 | 0.007 | 0.160 | 0.108 |
| 1 1/4 | 1.375 | 0.030 | 0.007 | 2.500 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1 3/8 | 1.500 | 0.030 | 0.007 | 2.750 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1 1/2 | 1.625 | 0.030 | 0.007 | 3.000 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1 3/4 | 1.875 | 0.045 | 0.010 | 3.375 | 0.045 | 0.010 | 0.213 | 0.153 |
| 2 | 2.125 | 0.045 | 0.010 | 3.750 | 0.045 | 0.010 | 0.213 | 0.153 |
Materials
- Plain steel
- Zinc-plated steel
- Stainless steel
- Brass
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (SAE Flat Washers (Inch Series)) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
What do the #4–#12 sizes on an SAE washer chart mean?
They are numbered-series sizes — the gauge designations of the machine screws and small bolts the washers accompany — sitting below the fractional bolt sizes on the same chart. A #4 is the smallest tabulated size, and the fractional series takes over from 1/4" upward. When ordering, state the size exactly as your drawing does (numbered or fractional); the washer inside diameters are tabulated for each so the match is unambiguous.
Can SAE washers be substituted where a USS washer is specified?
Not one-for-one. At the same nominal bolt size the SAE washer is narrower and thinner, so it delivers less bearing area — under load on a soft substrate or an oversized hole it can embed or pull into the opening where a USS washer would have held. The reverse substitution (USS where SAE is specified) usually fits the bolt but may foul adjacent features or moving parts. Substitute only with the joint's clearance and bearing requirements checked, and record the change on the drawing.
What is the MOQ and lead time for this washer type?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Common sizes in this washer type are widely stocked; confirm the exact schedule against quantity and size mix at quotation.
What should an RFQ for this washer type state?
State the series (USS or SAE), the nominal bolt size it must fit, material and finish requirements (plain, zinc-plated, stainless, or brass), any hardness requirement, required certificates such as a mill test report per EN 10204 3.1, and quantity per size — plus destination country.
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support