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Thread Types
Mechanical Properties
Technical FAQs
Technical FAQs
  1. Are rolled threads stronger than cut threads?
    Rolled threads can typically be 10-20 percent stronger than cut or ground threads primarily due to the cold working and displacement of material rather than the cutting or removal of material. Thread rolling can also add to the fatigue and wear resistance, and increase smoothness and hardness of the threads as they are planished in the forming process. Other advantages may include higher manufacturing speeds and reduced waste.
  2. Do all fasteners need to be baked after plating?
    No, not all need to be baked. The primary reason that fasteners are baked after the plating process is to help eliminate the possibility of hydrogen embrittlement, an undesirable time delay deterioration of the base metal after the plating process. The phenomenon can occur on fasteners over a certain hardness which makes product grades 10.9 and above susceptible. Although baking is an acceptable treatment it cannot completely eliminate the possibility of this undesirable condition. Care should be given when baking to avoid disrupting the original intended tensile strength of the fastener by approaching the tempering temperature.
  3. Why are bolts marked "8.8" mated with nuts marked only "8"?
    The matching bolt and nut grades identifying markings are designated differently to demonstrate the strength relationship of the two components. Due to the advent of mass assembly it is an acceptable practice for the matching nut to be the stronger component. The logic behind this theory is that during assembly if the nut is stronger the joint should fail immediately and thus reduce subsequent field failures. More specific information as to this relationship can be found in Section 10 of our catalog on pages 10-1020 and 10-1021.
  4. Is A4/316 stainless better/stronger than A2/304 stainless?
    Not necessarily. Both A4/316 and A2/304 are primarily indicators of the chemical composition of these Austenitic ( not heat treatable ) fasteners. They get their ultimate mechanical strength from the cold working and forming process. That’s why stainless fasteners have an additional markings such as 50, 70, 80 to indicate their mechanical strength as well as their chemical properties. A2 may be magnetic and is corrosion resistant, A4 must not be magnetic and has the addition of being acid resistant. See our catalog pages 10-1023 and 10-1024 in Section 10 for more details.
  5. What does "DIN" mean?
    A direct translation to DIN is Deutsches Institute fur Normung or better understood as German Institute for Standardization. DIN is the internationally recognized consensus standards body of Germany. Well established before ISO the DIN nomenclature and practices continue to be prevalent in the fastener industry.
  6. What are "PG" Threads?
    PG threads are a common form of metric thin walled conduit/electrical threads. The shallow 60 degree thread angle profile directly translates to Panzer Gewinde. Due to the shallowness of the thread profile the NoGo Thread Gage member is typically unthreaded.
  7. Which is more popular in Europe, BSP or BSPT?
    The popularity of British Pipe Thread conventions, straight or tapered, depends more on application and design. Whether BSP or BSPT they both have been adopted as metric type pipe threads. BSP is a straight thread similar to a fastener thread and does not seal on the thread surface but relies upon some sort of additional sealing element. BSPT is a tapered thread ( 1:16 or ¾” in. per foot )that goes into a straight or tapered hole and seals on the thread. American NPT thread is tapered so in the United States the BSPT thread is more familiar.
  8. Why are British fasteners so expensive?
    Expense is relative to the value gained. In 1974 England completed their formal year conversion to the metric system. Over the past 30 plus years the supply and demand of these obsolete parts has dwindled. Much of the technology that these parts were used in has long been replaced with new equipment using metric parts. Inventories have been depleted many styles, sizes, and materials are only available as Special Manufacture. We still maintain a good inventory and close contacts with our British vendors.
  9. Are B7 & 8.8 equal in strength?
    To many, chemistry is equivalency. Add to that the matter of proprietary alloys within a classification of steels and the debate continues. However, how a material is processed can change its performance characteristics. Originally B7 and 8.8 can come from a similar base metal but B7 is mainly processed differently to give it its required heat resistance. Within the normal operating temperature range of 8.8 they have similar performance characteristics.
  10. How do you calculate the tap drill sizes in metric?
    Arriving at the tap drill size for general purpose metric screw sizes is easy and doesn’t require a chart. For tap drill sizes in steel the formula is simple: Subtract the pitch of the thread from the nominal diameter.
    Example: M6 x 1 6 minus 1 is 5 Tap drill size 5mm
  11. What does "B3B" mean on my print?
    "B3B"is a plating specification the breakdown goes like this. The first letter is the plating material, the middle number is the code number for the plating thickness , and the last letter refers to the final delivery appearance and/or passivation.

    This information can be found in our Catalog Section 10 on page 10-1031. In particular the B3B breaks down to :

    B (plating material) Cadmium
    3 (plating thickness) 8 microns or .0003 inch
    B (delivery appearance) Dull matte finish
  12. Are your hex head bolts made with a black oxide finish?
    While the normal delivery condition of fasteners may sometimes be referred to as Black Oxide, rarely is that the actual finish. It is generally used in a broad form to distinguish them from plated fasteners. The actual finish is more of a phosphate and oil ( phos & oil ) preservation. Actual Black Oxide and Parkerizing are proprietary finishes.
  13. What’s the difference between “proof load” and “tensile load“?
    Heat treaded alloy fasteners are designed to be stretched to a certain point to retain their clamping load. It’s up to the design engineer to establish which size fastener, how many, and how tight.
    Proof load: the stretching load allowed before deformation and or functional failure.
    Tensile load: The ultimate stretching load allowed before the bolt strips or fails. The proof loads of hex nuts are designed to exceed the tensile load of the matching hex bolts in support of the theory that the nuts should be the stronger component.
  14. Why are there fine threads?
    Fine thread have two advantages and many disadvantages. First they were thought to be stronger since the shallower thread disrupted the base metal less and provided a larger minor diameter. Second they offered finer dimensional and torque adjustments. However in real world manufacturing and handling applications general purpose fasteners lose some of these benefits due to complications related to inadvertent thread damage. It is recommended that the first choice for general purpose metric screw threads be standard pitch.
  15. Why are the pitch diameters on the GO and NOGO thread ring gages I ordered not the same as the bolt I’m evaluating?
    The gages you ordered are Working Gages intended to qualify a specific thread size and tolerance class, not the gage. The gage must have a specific and appropriate pitch gage tolerance its self to allow the proper clearance and form a basis for re-calibration.
  16. When using a NOGO thread gage they say the “gage should not accept the parts“ - what exactly does that mean?
    This is a simple question that has complicated answers. First there must be an agreement on the sampling size before the gage come out of its case. Then there are quite a few different standards both national and international that address this situation and range from a simple ‘not more than two threads’ to a “specific torque applied with resistance felt along the thread after the first two threads”. ASME metric gauging practice allows the part to totally pass through the NOGO ring providing the operator can feel a definite drag once they go past the first two threads. There are charts that are diameter sensitive and indicate the maximum torque that should be applied to sense this drag. These charts are used so that parts aren’t resized with the gage. Independent of which convention is used it is ultimately the responsibility of the buyer and user to qualify the parts as acceptable before use in their particular application.
  17. Is there a special oversized gage to gage parts after plating?
    Unless agreed upon before hand, metric parts should still gage within the normal thread limits of the original classification. Care should be given when plating existing product that it doesn’t exceed the maximum condition after plating.
  18. How are sheet metal screw threads different than wood screw threads?
    Although they may look similar at first there are differences that make them work properly in their intended materials. Sheet metal screw threads are intended to displace the base metal and form a sort of nut thread relationship into the hole in the base metal. Wood screws have a deeper, sharper thread profile that is intended to cut into the wood fibers. The wood screws thread pitch is slightly larger and has a more pronounced taper on the end. There are also specialized proprietary wood screw threads that are intended for the newer type composite and polymerized wood products.
  19. How are British screw threads different than American?
    Although the nominal sizes are similarly labeled the main difference lies in the thread profile and resultant relationship of the pitch diameters. Both systems identify their nominal diameters primarily by factional inches however, the British use a 55 degree thread angle with radiused root and crest. The customary American profile is 60 degrees with angular root and crest. Even though you may find a diameter and pitch combination that may seem to match it should not be used. The resultant assembly will be significantly weaker since there will be excess play due to the different angles and the threads will be binding on the root and crest rather than the pitch diameters.
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