ISO 80369-1:2025 Annex B - Demonstrating Non-Interconnectability

Annex B as a three-stage gate

Annex B is normative: it defines how objective evidence of non-interconnectability is produced. The process (Figure B.1) is sequential - dimensional analysis first; if a potential misconnection remains, the physical misconnection test; if a misconnection is still shown, an ISO 14971 risk analysis decides acceptability. Each stage can close the file: a clean dimensional result needs no testing, and an accepted risk needs no redesign.

Stage 1a: identifying contactable surfaces

A contactable surface (3.6) is any surface of the connector that can physically contact and potentially interact with any surface of a mating connector. Clause B.3.2 requires the inventory to go beyond the obvious sealing faces: internal and external diameters, thread crests (major and minor), ribs and lug (cam) features, end faces, shoulders, chamfers, radii and cylindrical edges. Augmentation structures - features added to prevent misconnection - must also enter the analysis, because they can create, not only prevent, mating opportunities.

For a typical fixed-collar cone the evaluated structure spans the full cone surface from tip outside diameter to root outside diameter, the thread major and minor diameters where present, and the fluid-path bore (Figures B.2 to B.5). For ribbed or lugged connectors the effective diameter, root diameter and the gaps between features are all evaluated.

The four interface types

The analysis is organised around four generic interface pairings (Figures B.6 to B.9). The pairing determines which Table B.2 interference limit applies later, so the classification must be settled before any calculation:

• Full diameter to full diameter.
• Full diameter to full thread.
• Full diameter to lug (cam) thread.
• Thread to thread.

Stage 1b: the clearance, transition and interference calculation

For every candidate ID/OD pairing, relationship A is calculated at MMC (A = di,min - do,max) and relationship B at LMC (B = di,max - do,min). Table B.1 then gives the decision logic:

• A greater than 0.05 mm and B positive: clearance in all material states - no misconnection possible.
• A positive but 0.05 mm or less: potential misconnection - very small clearances can bridge through interface friction, roundness deviation or trapped air.
• A zero or negative and B zero or positive: transition across the tolerance range - a misconnection will occur in some material states; physical testing is mandatory.
• A and B both negative: interference in all states - compare the absolute value of B with the Table B.2 limit for the interface type; if it exceeds the limit, the pair is judged non-interconnectable, otherwise testing follows.
• Zero results are treated as line-to-line contact, a special case of interference.

The Table B.2 interference limits

For materials with a flexural or tensile modulus of at least 700 MPa, the minimum interference that reliably prevents forced assembly is:

• Full diameter to full diameter: 0.284 mm.
• Full diameter to full thread: 0.400 mm.
• Full diameter to lug thread: 0.820 mm.
• Thread to thread: 0.400 mm.
• Note how lugged interfaces demand roughly three times the interference of plain diameters - compliant material can deflect a long way around a lug profile.

Stage 2: the misconnection test (B.4)

The physical test uses an interference test part (3.9) - a part physically representing the mating connector, moulded or machined from material with a modulus no more than 100 MPa above the connector minimum, with dimensions deliberately adjusted to realise the interference calculated in the analysis. Real production samples almost never sit at the worst-case dimensions, so the standard tells you to make the worst case happen on purpose.

Test parameters (B.4.6): conditioning at 20 plus/minus 5 degrees C and 50 plus/minus 10 percent RH for at least 1 hour; assembly at 70 plus/minus 1 N axial force applied at 10 plus/minus 1 N/s with 0.12 plus/minus 0.02 N-m torque (no more than 90 degrees of clockwise rotation), held for 10 plus/minus 1 s. The 70 N force represents the 50th-percentile adult assembly effort. The pair must then separate under its own weight or a 0.02 N force, whichever is greater - otherwise the connection is classified as a misconnection. Left-hand-thread evaluations reverse the rotation direction.

Stage 2b: the leak test (B.5)

If the assembled pair does not separate, a leak test quantifies what actually passes through: the assembly is filled with water from a syringe of at least 10 mL (ISO 7886-1) through no more than 15 cm of tubing, and the delivered versus retained volumes are weighed to give a water leakage percentage Lw. The rationale (A.2.10): a connection that looks engaged but leaks is an acceptable risk because no medium is misdelivered. The standard reminds manufacturers to assess the clinical relevance of water - high-viscosity clinical fluids change the leakage behaviour.

Stage 3: risk analysis and closure

A confirmed misconnection does not automatically fail the design; it triggers an ISO 14971 risk analysis focused on the severity of misdelivery (A.2.6). Annex E shows accepted cases, such as N1-to-L2, where the worst outcome is linking two infusion sources to each other. The file closes with documented objective evidence - analysis, test reports and risk conclusions - which is exactly the evidence set an assessor or purchaser will ask to see.

Laboratory execution notes

Two points decide most Annex B programmes in practice. First, metrology: MMC and LMC inputs must come from measured or properly toleranced drawings, not nominal CAD. Second, sample strategy: interference test parts are engineered artefacts, and their dimension adjustments and modulus verification should be documented as carefully as the test results themselves. We build both the axial-torque assembly stations (70 N, 0.12 N-m) and the gauge sets used to certify test-part dimensions, so the whole evidence chain stays within one calibration system.