USS Flat Washers (Inch Series)
USS-pattern flat washers for inch hardware — the wide-body series, 3/16" through 3" nominal bolt size, with a larger outside diameter and thickness than SAE at the same bolt size for greater bearing area and load distribution. Dimensioned per ASME B18.21.1 plain-washer tables.
Last updated: 2026-11
Specifications
USS (United States Standard) is the wide-body flat washer of the inch series. At any given bolt size it runs a larger outside diameter and a thicker section than the SAE pattern — a 1/2" USS washer measures about 1.375 in across at 0.086–0.132 in thick, against roughly 1.062 in and 0.074–0.121 in for the SAE counterpart — so it spreads the clamp load over more surface. That makes it the default choice wherever the joint, not the fastener, needs the bearing area: oversized or slotted holes, softer substrates, and general construction hardware. The size line runs from 3/16" up to 3" nominal bolt size, with inside-diameter, outside-diameter and thickness tolerances tabulated for every step. Most distributors stock USS washers plain, zinc-plated, in stainless steel, or in brass.
| Standard | ASME B18.21.1, inch-series plain washers (legacy USS series; older references cite ASME B18.22.1) |
|---|---|
| Size range | 3/16" – 3" nominal bolt size |
| Dimensions at 1/2" | ID 0.562 in × OD 1.375 in × 0.086–0.132 in thick |
| Tolerances | ID/OD +0.015 to +0.065 plus / −0.005 to −0.010 minus by size; thickness min–max per size step |
| OD character | Wider and thicker than SAE at the same bolt size — more bearing area for load distribution |
| Materials and finishes | Plain steel, zinc-plated steel, stainless steel, brass (common trade stocking range) |
| Typical use | Inch-series joints that need the bearing area: oversized holes or soft substrate, general inch hardware |
| 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) |
|---|---|---|---|---|---|---|---|---|
| 3/16 | 0.250 | 0.015 | 0.005 | 0.562 | 0.015 | 0.005 | 0.065 | 0.036 |
| 1/4 | 0.312 | 0.015 | 0.005 | 0.734 | 0.015 | 0.007 | 0.080 | 0.051 |
| 5/16 | 0.375 | 0.015 | 0.005 | 0.875 | 0.030 | 0.007 | 0.104 | 0.064 |
| 3/8 | 0.438 | 0.015 | 0.005 | 1.000 | 0.030 | 0.007 | 0.104 | 0.064 |
| 7/16 | 0.500 | 0.015 | 0.005 | 1.250 | 0.030 | 0.007 | 0.104 | 0.064 |
| 1/2 | 0.562 | 0.015 | 0.005 | 1.375 | 0.030 | 0.007 | 0.132 | 0.086 |
| 9/16 | 0.625 | 0.015 | 0.005 | 1.469 | 0.030 | 0.007 | 0.132 | 0.086 |
| 5/8 | 0.688 | 0.030 | 0.007 | 1.750 | 0.030 | 0.007 | 0.160 | 0.108 |
| 3/4 | 0.812 | 0.030 | 0.007 | 2.000 | 0.030 | 0.007 | 0.177 | 0.122 |
| 7/8 | 0.938 | 0.030 | 0.007 | 2.250 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1 | 1.062 | 0.030 | 0.007 | 2.500 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1-1/8 | 1.250 | 0.030 | 0.007 | 2.750 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1-1/4 | 1.375 | 0.030 | 0.007 | 3.000 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1-3/8 | 1.500 | 0.045 | 0.010 | 3.250 | 0.045 | 0.010 | 0.213 | 0.153 |
| 1-1/2 | 1.625 | 0.045 | 0.010 | 3.500 | 0.045 | 0.010 | 0.213 | 0.153 |
| 1-5/8 | 1.750 | 0.045 | 0.010 | 3.750 | 0.045 | 0.010 | 0.213 | 0.153 |
| 1-3/4 | 1.875 | 0.045 | 0.010 | 4.000 | 0.045 | 0.010 | 0.213 | 0.153 |
| 1-7/8 | 2.000 | 0.045 | 0.010 | 4.250 | 0.045 | 0.010 | 0.213 | 0.153 |
| 2 | 2.125 | 0.045 | 0.010 | 4.500 | 0.045 | 0.010 | 0.213 | 0.153 |
| 2-1/4 | 2.375 | 0.045 | 0.010 | 4.750 | 0.045 | 0.010 | 0.248 | 0.193 |
| 2-1/2 | 2.625 | 0.045 | 0.010 | 5.000 | 0.045 | 0.010 | 0.280 | 0.210 |
| 2-3/4 | 2.875 | 0.065 | 0.010 | 5.250 | 0.065 | 0.010 | 0.310 | 0.228 |
| 3 | 3.125 | 0.065 | 0.010 | 5.500 | 0.065 | 0.010 | 0.327 | 0.249 |
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 (USS 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
USS or SAE — how do I pick the right flat washer series?
Both are inch-series plain washers covering the same bolt sizes; they differ in body proportions. The USS washer carries a larger outside diameter and a thicker section at every shared size, so it distributes the clamp load more broadly — the choice where the hole is oversized, the substrate is soft, or the joint needs maximum bearing area. The SAE washer is narrower and thinner, made to fit tighter clearances around the fastener. Match the series to what the joint needs: bearing area versus clearance.
Are USS washers still covered by a current standard?
The USS designation itself is a legacy trade name, but the geometry is standardized: current ASME B18.21.1 covers helical spring-lock, tooth lock and plain washers in the inch series, and the USS/SAE flat-washer tables are carried there. Older literature and charts reference ASME B18.22.1, the earlier plain-washer standard — same families, so drawings citing either designation describe the same physical part. Order by series and nominal bolt size, and let the dimension table settle the rest.
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