TL;DR:<\/strong><\/p>\n The connection interface on a flexible shaft falls into a handful of recurring geometries, and each one demands different callouts on a drawing or measurement sheet.<\/p>\n Drawing callouts differ by type: a square drive needs only width-across-flats and depth, while a flanged interface needs a pilot diameter plus a full bolt pattern. Getting the callout type wrong is one of the most common reasons for a delivered part not seating correctly.<\/p>\n A measurement error at this stage propagates directly into a fit failure at assembly, so working through the interface in a fixed order avoids missed dimensions.<\/p>\n Calipers, a depth micrometer, and a bore gauge cover most of this work. Note tolerances as a range, not a single number. A hub bore is rarely a nominal value in practice.<\/p>\n Pro Tip:<\/strong> Sketch the mating hub cross-section by hand, even roughly, and mark every dimension with its measured tolerance. Attach a photo with a ruler in frame, or a STEP file if the hub is already modeled. A rough sketch with real numbers beats a clean drawing with assumed ones.<\/em><\/p>\n Flange-mounted coupling interfaces frequently reference SAE J620<\/a> or DIN 6281, which specify bolt circle diameter, pilot diameter, and flange thickness to keep motor and transmission housings compatible with a range of couplings. These standards work well when both the shaft supplier and the mating equipment manufacturer agree on which one governs the interface.<\/p>\n Many installations, particularly in industrial manufacturing applications<\/a> with confined mounting envelopes, require bespoke matching to a specific drive housing even where a nominally applicable standard exists, according to guidance on flexible-welle connection standards<\/a>. When a datasheet lists standards compliance, such as the flange dimensions noted in the ARCUSAFLEX product PDF, request the CAD model directly rather than re-deriving dimensions from a printed table. When it doesn\u2019t, plan for a custom adapter from the start.<\/p>\n Connection dimensions describe the interface, but they mean nothing if the shaft can\u2019t deliver rated torque through the installed geometry. Torque capacity drops as bend radius tightens, which is one of the most overlooked causes of undersized shaft selection despite perfectly matched connection dimensions.<\/p>\n Machine Design\u2019s coverage of flexible shaft installations<\/a> confirms that tight bend radii measurably cut torque capacity in confined routing, and recommends derating against supplier tables rather than the nominal straight-shaft rating. For synchronization shafts or valve override systems where bend geometry is fixed by the airframe or housing, that derating step belongs in the initial torque transmission<\/a> calculation, not as an afterthought once parts arrive.<\/p>\n A specification package that arrives complete on the first submission avoids the clarification cycles that add days or weeks to a quote. The following fields cover what most engineering teams need to include.<\/p>\n For precision or position-critical work, such as synchronization shafts in actuation systems, request tighter tolerance grades and specify runout and concentricity limits explicitly. General-purpose assemblies can typically work with looser bore and shoulder tolerances. Custom adapters generally carry longer lead times than stock connectors, so flag any expedited need at RFQ submission rather than after quoting begins.<\/p>\n Fielded installations reveal the same handful of specification errors repeatedly. Recognizing them before drawings go out saves a redesign cycle later.<\/p>\n BIAX asks for a defined axial datum, typically the shoulder or flange face, plus a single axial dimension (referred to as Lx on many flange datasheets) to establish insertion depth without ambiguity, consistent with the approach outlined in the ARCUSAFLEX datasheet<\/a>.<\/p>\n Pro Tip:<\/strong> Photograph the mating hub with a ruler placed against the bore and the hub\u2019s orientation clearly visible. A single labeled photo resolves more ambiguity than a paragraph of written description.<\/em><\/p>\n The connection interface\u2019s material and finish affect fit as much as its dimensions do. Shaft cores and adapters are commonly manufactured from carbon or stainless steel, chosen based on the corrosion resistance and fatigue life the application demands. Stainless variants add cost but hold tolerance better under repeated thermal cycling, which matters where a connection sees frequent actuation rather than a fixed installed position.<\/p>\n Surface finish at the mating diameter directly affects fit repeatability. A rougher finish on a shaft\u2019s insertion diameter increases effective clearance variation, since asperities compress differently on each assembly cycle. For interfaces that get assembled and disassembled repeatedly, such as service-access points on ground support equipment, a finer surface finish on both the shaft and hub reduces galling risk and keeps the measured bore diameter closer to nominal over the component\u2019s service life.<\/p>\n Plating or coating adds a dimension that\u2019s easy to miss on a drawing. A zinc or nickel plate thickness of even a few microns changes the effective diameter enough to bind against a bore machined to the base-metal dimension. When specifying a plated or coated connector, state whether recorded dimensions are pre-plate or post-plate, and note the plating thickness separately rather than folding it into the tolerance band. This single clarification prevents a disproportionate share of the \u201cfits on the bench, binds on the machine\u201d complaints that surface after delivery.<\/p>\n Operating conditions change a connection\u2019s effective dimensions after installation, which is why a fit verified at room temperature on a bench doesn\u2019t guarantee a fit in service.<\/p>\n Thermal expansion affects the shaft and hub differently when their materials differ. A steel shaft inserted into an aluminum housing, common in weight-sensitive aerospace applications, will see the bore expand faster than the shaft diameter as temperature rises, loosening a connection that measured tight at assembly. In the reverse temperature direction, that same pairing can tighten to the point of binding. Specifying the expected operating temperature range at RFQ stage lets the connection be matched with the right nominal clearance rather than a room-temperature fit.<\/p>\n Vibration acts on the connection differently than thermal cycling does. Sustained vibration, common in confined installation environments near engine or actuation hardware, tends to work fasteners loose and can cause micro-motion at a set-screw or keyed interface that gradually enlarges the mating bore through wear. A connection specified with a slightly tighter initial tolerance, or one using a positive-locking feature rather than friction alone, holds its dimensions longer under sustained vibration than a friction-only fit.<\/p>\n Neither effect shows up in a static measurement. Both belong in the RFQ\u2019s operating-condition notes alongside torque, RPM, and bend geometry, not left to be discovered after the first vibration or thermal test cycle.<\/p>\n Precise connection dimensions, submitted once and correctly, avoid the redesign cycle that costs far more time than the measurement itself. This matters most in synchronization and actuation systems, where a shoulder position off by a millimeter can mean a reworked bracket. Attach a sketch or STEP file when reaching out. It removes nearly all ambiguity from the first conversation.<\/p>\n \u2014 Uli<\/em><\/p>\n<\/blockquote>\n Biax-flexwellen engineers custom flexible shaft connections for design teams who need a matched fit the first time, not after two rounds of clarification. Submit a 2D drawing with critical dimensions and tolerances, a STEP file if you have one, and a labeled photo of the mating hub. That package alone is usually enough to start a quote without a follow-up call. State torque, RPM, and installation bend geometry alongside the drawing so the derating calculation happens before parts are cut, not after a fit test fails.<\/p>\n Review typical connection details and application examples on the flexible shaft applications page, then send your specification package through the BIAX contact page<\/a> to start a quote on a custom or standard configuration.<\/p>\n For flange geometry, consult SAE J620 or DIN 6281 directly for bolt circle and pilot diameter tables. For measurement practice on an unmarked or legacy hub, a representative manufacturer datasheet such as the ARCUSAFLEX PDF shows how axial datum and Lx dimensions are typically documented.<\/p>\n <\/p>\n\n
\nTable of Contents<\/h2>\n
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Connector Types and the Dimensions Each One Needs<\/h2>\n
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How Do You Measure a Mating Hub Accurately?<\/h2>\n
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Which Standards Govern Flange and Coupling Dimensions?<\/h2>\n
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How Bend Radius and Torque Change the Usable Connection<\/h2>\n
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What Belongs in an RFQ for a Custom Connection?<\/h2>\n
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BIAX Engineering Guidance for Specification Packages<\/h2>\n
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Materials and Surface Finish at the Connection Interface<\/h2>\n
![\"Materials](\"https:\/\/biax-flexwellen.de\/wp-content\/uploads\/2026\/09\/1788395957777_Materials-and-Surface-Finish-at-the-Connection-Interface-overview-diagram.jpeg\")
<\/p>\nTemperature, Vibration, and Connection Stability<\/h2>\n
![\"Thermal](\"https:\/\/biax-flexwellen.de\/wp-content\/uploads\/2026\/09\/1788395920142_Thermal-fit-changes-between-steel-shaft-and-aluminum-housing.jpeg\")
<\/p>\nAuthor Perspective: Why Precise Connection Dimensions Save Time<\/h2>\n
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Get a Custom Flexible Shaft Quote from BIAX<\/h2>\n
Primary Standards and Representative Datasheets<\/h2>\n
Sources<\/h2>\n
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Recommended<\/h2>\n
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Related Topics<\/h3>\n