Can Portland Bolt manufacture a 1" x 6" fully threaded A325 heavy hex structural bolt?

Bolts manufactured to the ASTM A325 specification have a fixed thread length for a given diameter, which is often shorter than other grades of bolts. For example, a 3/4″ diameter A325 has 1-3/8″ of thread and a 1″ A325 has 1-3/4″ of thread, regardless of the overall length of the bolt. Our structural bolts product page contains a table of thread lengths for each available diameter.

The A325 specification contains specific language limiting these bolts to these thread lengths. Section 1.5 of the specification reads as follows:

1.5 This specification is applicable to heavy hex structural bolts only. For bolts of other configurations and thread lengths with similar mechanical properties, see Specification A449.

However, the A325 specification also has a supplemental requirement (S1) that allows A325 heavy hex bolts to be fully threaded. The (S1) supplement states that A325 “bolts with nominal lengths equal to or shorter than four times the nominal bolt diameter shall be threaded full length.” In other words, if the bolt is longer than four times the diameter it cannot be fully threaded. Fully threaded A325 heavy hex structural bolts are stamped with “A325T” on the head of the bolt instead of “A325”.

So, does this mean that Portland Bolt will not manufacture with an A325 with extra thread that exceeds four times the diameter in length? No. We see A325 bolts with extended thread lengths specified by engineers all the time. ASTM specifications are guidelines that provide a buyer of a product with expectations as to the chemistry, strength, and configuration of a product they are purchasing. It is our responsibility to bring the issue of thread length to our customer’s attention and to let them know that technically, the correct bolt with extended thread should be ordered to the A449 specification. However, if the customer understands and still wants to proceed with an order of A325 bolts with extended threads, we will manufacture them.

In 2015, ASTM introduced a new structural bolt specification F3125. This specification is a consolidation and replacement of six ASTM standards, including; A325, A325M, A490, A490M, F1852, and F2280. Therefore, A325 is now a grade within the F3125 specification.  Under F3125 Supplementary Requirement S2, thread lengths can now be altered provided the A325 grade symbol permanently stamped on the head is followed by the letter “S” to indicate “Special”. Currently, ASTM A325 and ASTM F3125 Grade A325 coexist. Therefore, a fully threaded ASTM F3125 Grade A325 bolt longer than four diameters in length can be manufactured, provided the bolt is marked “A325S”, but under the existing A325 specification it technically cannot be made.
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10 comments

    @Hussain – Both the full thread and partial thread varieties are allowed by the AISC, so it will depend on if your application allows threads in the shear plane or not. It is not a question we can answer, it will be up to your project engineer.

    When a bolt passes through 3 1/2 inch plates of Steel I thought it was supposed to be a solid Shank and then the threads begin can a threaded bolt go all the way through with no damage to the components

    @Ken- It depends on the forces acting on the bolt. The designing engineer should determine if the threads can be in the shear plane. If they can, a fully threaded bolt should be fine. If not, then you’d need to use a bolt long enough that the threads can be excluded.

    @Gerardo- A325 bolts have different dimensions than A394 bolts, but yes, they have specific dimensional tolerances per ASME B18.2.6.

    Hello, I have a quick question regarding the strength tolerance according to threading length.
    how much would the strength of a bolt be reduced if the threaded part is longer. My actual case is an M12x150 hex bolt (half threaded), and I want to compare it to an M12x150 hex bolt (30 mm threaded). Is it possible to know the reduction in its mechanical strength?
    Many Thanks

    @Ali – It would depend a bit on the forces acting upon the bolt. In tension it shouldn’t make a difference, but if there are other factors at play it might. This is a bit above our level of expertise, you’d need to contact an engineer for a good answer to this.

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