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    Thread dimension and graphical design

    ​Technical guidelines for designing and documenting a Flowdrill connection

    Correct graphical representation of a Flowdrill connection is essential for clear communication between engineering, manufacturing and quality teams. This page provides standard guidelines for thread dimensions, drawing conventions and recommended annotations when documenting holes and threads produced by friction drilling and subsequent forming or tapping.

    Because Flowdrill connections differ from conventionally drilled holes, accurate presentation in CAD and technical drawings ensures consistent interpretation across OEMs, Tier 1s and machining partners.

    Why Flowdrill connections require specific drawing standards

    A Flowdrill joint is a thermally formed bush, and a thread that is created within the displaced material. This geometry cannot be correctly expressed using standard drilled-hole symbols alone.

    Precise graphical documentation helps to:

    • Ensure the required bush height is respected in production
    • Prevent incorrect machining (e.g. thinning the bush after forming)
    • Avoid misinterpretation of tolerances or thread engagement length
    • Provide clarity for suppliers unfamiliar with friction drilling

    CAD and model availability

    Many engineers select standard features directly from a CAD library. Since Flowdrill geometries are not yet included in common online libraries, individual STEP files can be requested from Flowdrill.

    These STEP models reflect the correct bush geometry, internal thread length and recommended tolerances.

    Standard drawing presentation

    The sketches below represent a typical drawing setup for Flowdrill connections. They include indications for:

    • Bush height
    • Minimum engagement length
    • Thread tolerance class
    • Flat surface requirements
    • Tool-based production notes
    • Required torque values (if applicable)

    Section A-A

    A typical cross-section shows:

    • Formed bush height (e.g. 6.50 mm minimum, depending on material thickness and tool diameter)
    • M-thread produced by Flowdrill ØX.X and roll forming tap
    • Requirement for flat surface, no burrs
    • Correctly dimensioned internal thread length
    • Nominal thread (e.g. M6 × 1 – 6H)
    • Minimum tightening torque (e.g. 7.2 Nm)
    • Alignment and spacing dimensions for mating components
    • Minimum distance around the bush (e.g. 9.0 mm) for proper material flow

    This section view ensures the manufacturer understands that the thread is fully contained within the formed bush and not inside the original sheet thickness.

    Recommended notes for drawings

    Include the following notes to avoid ambiguity:

    • Hole and thread produced by Flowdrill ØX.X and roll forming tap.
    • Bush height must not be reduced after forming.
    • Flat, burr-free surface required before drilling.
    • Length to be achieved by pilot hole ØX.X or via friction drilling depending on tool specification.

    These notes prevent downstream operations from altering the functional geometry of the bush.

    Need CAD files or drawing support?

    If you require STEP models, customised drawing guidelines or help integrating Flowdrill connections into your CAD library, our engineering team can assist. Provide your required diameter, material and application, and we will supply the correct geometry.