FAQs

Selection guidance

• Can I rely on adhesive datasheet compatibility information for my substrate?

  No – datasheets are helpful starting points only. They don’t account for surface condition, coatings, peel‑ply texture, bondline thickness, or fastener geometry.

  Always verify that the adhesive delivers adequate performance for your specific bighead fastener, substrate surface, and loading conditions.

• Can I use the same adhesive we already use elsewhere in our product or process?

  Often, yes – but don’t assume equivalent performance with fastener bonding. Adhesives that perform well for panel bonding, brackets, or structural bonding may behave differently for surface‑bonded fasteners, where load introduction and stress distributions are localised.

• Do I need to specify an ISO 4753 end-form for every bigHead stud product?

  No. The standard as‑rolled (RL) end‑form is suitable for most simple manual nut‑fitting applications.

  You only need ISO 4753 end‑forms if you’re looking to improve nut lead‑in, reduce cross‑threading risk, or need a high level of self-alignment, particularly in repeated or automated assembly.

• Do ISO 4753 end‑forms change the strength or performance of a bigHead stud (M1/ SM1) product?

  No. ISO 4753 end-forms do not affect weld load limit (WLL), fixing load limit (FLL) or recommended tightening torque values.

  All performance characteristics for end-form customisations are inherited from the standard M1/SM1 product. The end‑form affects physical behaviour, not structural capacity.

• Do washers or flanged screws affect screw length selection?

  Yes. Any component between the screw head and the collar adds to the installation stack thickness and must be included in the calculation.

• Does choosing PF or PC reduce the usable thread length?

  Yes – slightly, for a given nominal thread length (L).

  All ISO 4753 end‑forms introduce a short length of incomplete thread (Lu) at the stud end, which reduces the usable thread length (Le).

  PF and PC also increase the overall stud and overall bigHead fastener length due to the added pilot feature.

  These dimensional effects are standardised by thread size, and do not affect load ratings or tightening torque values.

• How do I know if my screw is long enough for a sighted collar?

  Ensure the screw length meets or exceeds the required minimum engagement: L + installation stack + 1.2 mm (if fastening from the Head side).

  The examples in this guide show how to calculate it.

• Is the strongest or stiffest adhesive always the best choice?

  No. For surface‑bonded fasteners, the balance between stiffness and flexibility is often more important than peak strength.

  Over‑stiff adhesives can increase stress concentrations, particularly on thin or flexible substrates. Tougher or more compliant adhesives may reduce peak stresses and improve durability under cyclic or peel‑sensitive loading.

• My application requires a specific engagement length. Can I request a custom collar design?

  Yes. bigHead offers custom collar options – including closed, sighted, length variant, and hybrid options. We can help you choose the optimal collar customisation for your application.

• Should I always do a pull-off test when selecting an adhesive, or are there other tests I can use?

  Pull‑off (axial) tests are useful for identifying bonding issues, but they’re not the only way to assess surface-bonded fastener performance.

  Choose test methods that reflect how the fastener is loaded in use, and don’t rely on a single set of pull-of results.

  For information on choosing tests and interpreting results, see our guide to evaluating fastener installation strength.

• What happens if the screw is too long in a blind collar?

  The screw will bottom out against the closed end, deforming or damaging the bigHead. This is considered misuse and may result in product failure.

• What is the practical difference between CH, PF and PC end-forms?

  The difference is how much alignment and guidance each end‑form provides during different operations.

  • CH (chamfered end) improves basic nut lead‑in and self‑seating without increasing the stud length.
  • PF (pilot point, flat) provides an extended straight pilot that captures a nut earlier and more reliably during manual assembly.
  • PC (pilot point with truncated cone) adds a tapered pilot that actively guides nuts into alignment, or stud-ends into other components, ideal for automation or tight tolerances.

  All three are defined by ISO 4753 and are compatible with bigHead M1/SM1 studs.

• When is validation testing necessary for selecting an adhesive?

  Whenever fastener performance is critical, substrates or surface conditions vary, or production or service environments are demanding.

  Testing should use application‑representative materials, surface preparation, bonding processes, and loading modes.

• Why can’t I specify ‘flat end’ or ‘dog point’ for bigHead fasteners?

  Standard as-rolled (RL) and chamfered (CH) end-forms can feature a slightly recessed or dimpled stud-end.

  Flat point (FL) and dog point (SD/LD) can look similar to the above – but they are not suitable for bigHead studs that receive a nut.

  Flat point (FL) is intended for screws that bear against a surface. Dog points (SD/LD) are intended for screws that locate into holes or slots. Neither supports reliable nut engagement on a stud.

• Why is tip clearance (Lu) different for each thread size?

  The clearance allowance scales with thread diameter and pitch to maintain sufficient deformation protection. Larger threads require greater tip clearance.