Extra Thick F436 Washer
What It Does
When a connection uses oversized or slotted holes, an extra thick hardened washer bridges the opening and adds bearing capacity a standard washer cannot. It shares the outside and inside diameters of a standard circular washer but is thicker, at 5/16″, giving additional bearing area for high-load applications. Extra thick hardened washers are available in diameters from 1/4″ through 4″ under ASTM F436, though larger sizes may require custom manufacturing.
Why the Added Thickness Matters
Oversized and slotted holes are common in structural steel, where they give erectors the tolerance needed to align members and land bolts in the field. That extra hole clearance, however, means a standard washer can flex or partially deform into the opening under full bolt tension, and it leaves less solid material bearing against the connected steel. The greater thickness of an extra thick washer resists that deformation and maintains a reliable bearing surface across the larger hole, which helps the connection develop and hold its specified pretension.
When to Use an Extra Thick Washer
An extra thick F436 washer is specified where the connection uses oversized or slotted holes and the design or the applicable structural bolting requirements call for the added thickness. It is not a general-purpose substitute for a standard washer on standard-hole connections. Because marketplace availability is limited and some washers sold as extra thick do not meet the 5/16″ dimension, it is important to specify the required thickness clearly when ordering.
Finishes and Material Types
Extra thick F436 washers are available in plain and hot-dip galvanized finishes, in Type 1 and Type 3 material as required by the assembly. Larger diameters are often manufactured to order. The finish and material type should match the bolt and nut used in the connection.
Extra Thick Washer Dimensions
| Nominal Washer Size | I.D. min | I.D. max | O.D. min | O.D. max | Thickness Std min | Thickness Std max | Thickness X-Thick min | Thickness X-Thick max | Clipped Min Edge Distance (E) |
|---|---|---|---|---|---|---|---|---|---|
| 1/4″ | 0.281″ | 0.313″ | 0.593″ | 0.657″ | 0.051″ | 0.080″ | … | … | 0.219″ |
| 5/16″ | 0.344″ | 0.376″ | 0.656″ | 0.720″ | 0.051″ | 0.080″ | … | … | 0.281″ |
| 3/8″ | 0.406″ | 0.438″ | 0.781″ | 0.845″ | 0.051″ | 0.080″ | … | … | 0.344″ |
| 7/16″ | 0.469″ | 0.501″ | 0.890″ | 0.954″ | 0.051″ | 0.080″ | … | … | 0.406″ |
| 1/2″ | 0.531″ | 0.563″ | 1.031″ | 1.095″ | 0.097″ | 0.177″ | 0.305″ | 0.375″ | 0.438″ |
| 9/16″ | 0.625″ | 0.657″ | 1.156″ | 1.220″ | 0.110″ | 0.177″ | 0.305″ | 0.375″ | 0.500″ |
| 5/8″ | 0.688″ | 0.720″ | 1.281″ | 1.345″ | 0.122″ | 0.177″ | 0.305″ | 0.375″ | 0.563″ |
| 3/4″ | 0.813″ | 0.845″ | 1.436″ | 1.500″ | 0.122″ | 0.177″ | 0.305″ | 0.375″ | 0.656″ |
| 7/8″ | 0.938″ | 0.970″ | 1.718″ | 1.782″ | 0.136″ | 0.177″ | 0.305″ | 0.375″ | 0.781″ |
| 1″ | 1.063″ | 1.126″ | 1.937″ | 2.063″ | 0.136″ | 0.177″ | 0.305″ | 0.375″ | 0.875″ |
| 1-1/8″ | 1.188″ | 1.251″ | 2.187″ | 2.313″ | 0.136″ | 0.177″ | 0.305″ | 0.375″ | 1.000″ |
| 1-1/4″ | 1.375″ | 1.438″ | 2.437″ | 2.563″ | 0.136″ | 0.177″ | 0.305″ | 0.375″ | 1.094″ |
| 1-3/8″ | 1.500″ | 1.563″ | 2.687″ | 2.813″ | 0.136″ | 0.177″ | 0.305″ | 0.375″ | 1.219″ |
| 1-1/2″ | 1.625″ | 1.688″ | 2.937″ | 3.063″ | 0.136″ | 0.177″ | 0.305″ | 0.375″ | 1.313″ |
| 1-3/4″ | 1.875″ | 1.938″ | 3.312″ | 3.438″ | 0.178″ ᴮ | 0.28″ ᴮ | 0.305″ | 0.375″ | 1.531″ |
| 2″ | 2.125″ | 2.188″ | 3.687″ | 3.813″ | 0.178″ ᴮ | 0.28″ ᴮ | 0.305″ | 0.375″ | 1.750″ |
| 2-1/4″ | 2.375″ | 2.438″ | 3.937″ | 4.063″ | 0.24″ ᶜ | 0.34″ ᶜ | 0.305″ | 0.375″ | 2.000″ |
| 2-1/2″ | 2.625″ | 2.688″ | 4.437″ | 4.563″ | 0.24″ ᶜ | 0.34″ ᶜ | 0.313″ | 0.375″ | 2.188″ |
| 2-3/4″ | 2.875″ | 2.938″ | 4.937″ | 5.063″ | 0.24″ ᶜ | 0.34″ ᶜ | 0.313″ | 0.375″ | 2.406″ |
| 3″ | 3.125″ | 3.188″ | 5.437″ | 5.563″ | 0.24″ ᶜ | 0.34″ ᶜ | 0.313″ | 0.375″ | 2.625″ |
| 3-1/4″ | 3.375″ | 3.500″ | 5.875″ | 6.125″ | 0.24″ ᶜ | 0.34″ ᶜ | 0.313″ | 0.375″ | 2.875″ |
| 3-1/2″ | 3.625″ | 3.750″ | 6.375″ | 6.625″ | 0.24″ ᶜ | 0.34″ ᶜ | 0.313″ | 0.375″ | 3.063″ |
| 3-3/4″ | 3.875″ | 4.000″ | 6.875″ | 7.125″ | 0.24″ ᶜ | 0.34″ ᶜ | 0.313″ | 0.375″ | 3.313″ |
| 4″ | 4.125″ | 4.250″ | 7.375″ | 7.625″ | 0.24″ ᶜ | 0.34″ ᶜ | 0.313″ | 0.375″ | 3.500″ |
| Footnotes: A — Clipped edge E shall be not closer than 7/8 of the bolt diameter from the center of the washer. B — 9/16″ nominal. C — 1/4″ nominal. D — Nominal washer sizes are intended for use with fasteners of the same nominal thread size. | |||||||||
Availability
Extra thick hardened washers have limited marketplace availability. Large diameters and custom sizes are manufactured to order.