Are washers required to be used with an A325 or A490 structural bolt?
It is known that the required grade of washer to be used with an A325 or A490 structural bolt is an ASTM F436 hardened washer, however whether or not a washer is required to be used in a given application is often brought into question. The purpose of using a flat washer with a bolt is to provide a smooth bearing surface under the head of the bolt and / or nut. There are different grades and styles of washers, which may differ in their thickness and outside diameter, providing a larger or smaller bearing surface. Per the ASTM A325 and A490 specification, they are specific to the grade of washer that is recommended, however it is not stated that a washer is required.
Although the ASTM A325 and A490 specifications do not require the use of a washer, there are a few circumstances where we know for sure that F436 hardened washers are required. When using A490 structural bolts, the strength of the material being connected can determine whether or not a washer should be used. Specifically, if the material being connected has specified minimum yield strength of less than 40 ksi, a washer should be used. According to the AISC 13th Edition, page 16.2-40:
“When ASTM A490 bolts are pretensioned in connected material of specified minimum yield strength less than 40 ksi, ASTM F436 washers shall be used under both the bolt head and the nut”
It is worth noting that an A490 strength, round head tension control bolt who’s head meets the bearing surface diameter requirements of ASTM F1852, does not require a flat washer under the head. The only other circumstance where a washer is required is if the hole in which the bolt is being inserted is oversize or slotted. The washer requirements for this situation are found in Table 6.1 in the AISC 13th Edition, page 16.2-41, which is summarized below.
| ASTM Grade and Diameter | Hole Type in Outer Ply | Required Washer |
|---|---|---|
| A325 or F1852 (½" - 1½") | Oversized or Short-Slotted | ASTM F4361 |
| Long-Slotted | 5/16" thick plate washer or continuous bar2, 3 | |
| A490 (≤ 1") | Oversized or Short-Slotted | ASTM F4361 |
| Long-Slotted | 5/16" thick plate washer or continuous bar2, 3 | |
| A490 (> 1") | Oversized or Short-Slotted | 5/16" thick ASTM F4362, 4 |
| Long-Slotted | ASTM F436 with a 3/8" thick structural grade plate washer or continuous bar2 | |
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Hi ,
Please provide your valuabe quote for the below item(s) with availability and lead time.
QTY
1.0000 32107B02A PADEYE,WOOLSLAYER,32107B02A,2.5 T WLL,C/W CLAMP PLATE AND 4 EA 3/4 DIA A325 BOLT W/FLAT WASHERS AND LOCKNUTS,GALV ASTM A123,C/W CERTS
@Song- Thank you for the inquiry – one of our salespeople will contact you shortly.
Are there any stainless steel F436 washers, or equivalents?
Thanks
@David- We are able to supply commercial 304 or 316 washers if austenitic stainless is what you are looking for, or we might be able to supply heat treated 410 washers if ferritic is acceptable. Neither are “equivalent” to F436, but might work depending on your application.
If slotted holes or oversize holes occur on the inner ply and not on the outer ply, is thick washers for 1 1/8Ø A490 bolt still required?
@Darrel- If the washer is only in contact with a standard size hole, and not an oversize hole, my assumption is that no oversized/thick washer is required. However, you might want to run this past your design or structural engineer to be certain.