What are full thread and half thread fasteners?


全ねじ 半ねじって full thread and half thread bolt

    In fasteners industry, male fasteners have 2 thread patterns which are Fully thread (Full-thread) and Partially thread (Half-thread). Then, what are their differences, and which one should we select for the project?

    Let’s start with Fully thread (Full-thread), this is a pattern refer to the fasteners which have threads run entirely from under the head to the tip with no grip length or thread-free portion.

    Fully thread will provide grip strength, once it fastened, mounting pressure will spread along the entire thread. This full thread suited for application where grip strength is critical concern comparing to alignment and shear strength. To be fully threaded, tension that placed on the bolt will not only on the bolt but will spread to entire structure (Material or object where it fastened to), so it can withstand with greater forces than partially thread one.

As we mentioned its strong points, there are also weak points of full thread as well. As it is fully threaded, made it weaker to shear force or the work where alignment is involved.

Mostly you will see fully thread bolt in the car panel, furniture, or critical machine part.

    Now, let’s talk about Partially thread (Half-thread), this is a pattern refers to fasteners which have threads run partially through some point of the bolt shank to the tip. Where remaining the rest to be gripping length and thread-free portion.

    Half thread will provide less grip strength as thread lengths are lesser, made mounting pressure that spread to the material or object also lesser. It is more suited for application where shear strength and alignment are involved. Non-threaded part (Bolt shank) means, there is no weak point that leads to cracking or bending.

Half thread fasteners are mostly used for application where bolt is inserting through the object and fasten them at the end with female nut and likely to be adjust or unfasten as threads area are fewer than full thread one.

You will see half thread bolt more often than full thread bolt, it can be found in any places like water pump, flange, bench, car parts, machine and etc.

Tips : In manufacturing industry, if we are going to get a bolt for example “Please give me a 4.8 Hex bolt M10x50” without saying full or half thread. This generally will be “Half-thread” as common.
    So, if you are new to manufacturing industry, please be careful about this issue. Also, if you really need half or full thread, it is better to inform the fasteners maker or distributor about your requirement to prevent misunderstanding.

Remember that, more information you provide, more accurate product as your expectation you will get.

Please check my previous blog about What we have to know when we request a quotation for fasteners product? For further information


Then, How can we know the half thread length for the bolt?

    As you might read introduction of half thread bolt as above already, then what about thread length of half thread bolt, how long it will be, how can we know? I will give you very useful guide to calculate this!

    For Metric hexagon bolt, there is be very simple formula as below to calculate without calculator needed, just basic mathematics.

Formula to calculate thread length for half-thread fasteners :

1.)    For bolt length ≤125mm : (Nominal size X 2) + 6

        a.       For example, Hex bolt M8x50, will have a thread length : (8x2)+6 = 22mm

2.)    For bolt length ≥130mm : (Nominal size X 2) + 12

        a.       For example, Hex bolt M12x150, will have a thread length : (12x2)+12 = 36mm

3.)    For bolt length ≥220mm : (Nominal size X 2) + 25

        a.       For example, Hex bolt M16x240, will have a thread length : (16x2)+25 = 57mm

    How was that sound, quite simple isn’t it? Just remember this formula and calculate in your mind will make you be able to promptly reply to your customer when they ask for the thread length for hex bolt.       

Anyway, above formula is used for standard hex bolt only. There are cases that thread length will be varied as well as custom thread length as customer requirement also possible.

Also, not all of the bolt lengths are going to have a half thread selection. The standard bolt length must be equal or more specific length as below example for each size as JIS B-1180(Hexagon bolt).


“s” which is written in the size refers to bolt thread length

Ex. M6x25x18s (This bolt has a thread length =18mm with total length = 25mm)

Available half thread selection for each size

≥M6x25mm   (M6x25x18s)

≥M8x30mm   (M8x30x22s)

≥M10x30mm (M10x30x26s)

≥M12x35mm (M12x35x30s)

≥M14x40mm (M14x40x34s)

≥M16x45mm (M16x45x38s)

≥M18x50mm (M18x50x42s)

≥M20x50mm (M20x50x46s)

≥M22x60mm (M22x60x50s)

≥M24x65mm (M24x65x54s)

That’s all for the thread length of hex bolt in JIS B-1180, I hope you enjoyed this content and be able to understand full and half thread fasteners differences as well as thread length information for half thread bolt.

Please stay tune with us for next content. Thank you so much for reading and follow our blog.



Written by,

                                                                                                      Mr.Nuttapol Sirilert

                                                                                                 International Sales Team

                                                                                                    Hanshin Neji Co.,Ltd.