What is a Bolt Blank?

From time to time our friendly estimators may mention that we are going to make your order using bolt blanks. But what is a bolt blank?

In order to help facilitate small runs of custom bolts and rush orders, Portland Bolt stocks bolt blanks. Bolt blanks are headed bolts that have not been threaded yet. Stocking these semi-finished parts allows us to quickly cut a blank to the required length (up to 36” long) and cut-thread the necessary amount of thread. They allow us to save time on heat treated grades, such as A325, because they can be heat treated after heading, but before we cut to length and thread. On non-heat treated grades they still offer a time savings, by allowing us to bypass the heading operation for you order.

For smaller runs, blanks can save you money as well. With smaller quantities of custom parts, one of the biggest costs can be setup costs. Since these bolts have already been headed, that setup cost is spread out over more than just the parts you ordered. For blanks that require heat treating (A325, A449), minimum heat-treating costs would come into play for small quantity orders, but are avoided when using blanks. Fixed testing costs for these grades are extreme when manufacturing small quantities, but are minimized when spread amongst a large run of blanks.

We stock blanks in diameters ranging from ½” through 2” depending on the grade. With the creation of the F3125 specification, we now carry A325 blanks with two different head markings, your standard “A325” and “A325S”. For more information on the “A325S” marking, please refer to this FAQ: Why are the heads of my A325 bolts marked with the letter “S”?

Portland Bolt has the following head styles and grades in stock:

Standard Hex Heavy Hex Square Head Timber Bolt
A307 Grade A
F1554 Grade 36
F1554 Grade 55
F1554 Grade 105
F3125 Grade A325
F3125 Grade A325S
F3125 Grade A490

If your project requires headed bolts in a thread pitch or tolerance that we are unable to provide, custom headed blanks in virtually any grade can be made for you to thread.

Our experienced estimators will determine if using a bolt blank is the fastest or most economical method of manufacturing your order. If you have any questions about bolt blanks or anything else, please feel free to give one of our team members a call and we will be happy to help.

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    What is the standard oversize diameter between the blank diameter and the finish shank diameter? Example if an A325 bolt is requested with a shank diameter of 1.4999″ LC6 fit, will the nominal bolt blank of 1.5″ allow for cleanup to 1.4999″ because the forging is oversized?
    Do you have a chart or formula for blank diameters?

    Does the blank oversizing increase as length increases since straightness may require more material to cleanup properly?

    @Ryan- The allowance for body diameter on 1-1/2 diameter A325 bolts is 1.470″ to 1.531″. The tolerance for diameter on the raw steel is 1.486 to 1.514. Unless we manufactured them specifically from oversized steel, we couldn’t guarantee an oversized shank. The diameter of the bar does not change as the blank gets longer. We do have them machined straightened after heat treat, but a little camber is still allowed. 0.008″ of camber per inch of length for bolts 12″ to 24″ in length.

    @Paul- the strongest off-the-shelf grade you will find in a hex headed bolts is SAE J429 grade 8. There is a higher strength grade, ASTM A574, but it only covers socket head cap screws. Either way, if a blank is what you need, it will likely be a special anyway, in which case we can discuss options. One of our salespeople will be contacting you shortly.


    Do you provide M24 by Minimum 50 long Plain Steel Bolt Blanks?

    If so what is the minimum quantity and what sort of delivery time as I have two Rolls Royce Tools stopped waiting for these.

    @Derek- Apologies, but we are unable to produce any metric fasteners. If you can accept a soft conversion to 1-8 we can help, but if they must be M24, we will have to pass.

    Hey there,

    You may have already heard from someone at my organization, but I am new here and heading up the engineering department at Acculign here in Portland. We are interested in bolt blanks to use in a press-fit assembly, where we require a bolt head. I am looking for more information about the blanks. Do you have a drawing of the smallest blank available? Your site says 1/2″, we are presently using 3/8″ bolts but may be able to utilize the 1/2″ to solve our problem. Are they available plated? What is the cheapest grade available? We do not require a high strength parts primarily the functionality. Please get back to me at your earliest convenience. Thanks for your time!

    Wylie- We are a custom bolt manufacturer, so we can make your bolt blanks to any grade and with a few different plating options. 1/2″ is the smallest size we can manufacture, and ASTM A307A is likely your least expensive option. You can look at a drawing on our website, I will also follow up with an email directly to you. https://www.portlandbolt.com/products/bolts/hex/

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