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Engineering data · GD&T

Concentricity and Coaxiality in Sensor Housings

By Yu Lianbo — Tooling Design Engineer

Why does concentricity matter so much on a sensor housing?

Because the sensing element and the mounting interface share an axis. If the bore and the mounting diameter drift apart, the sensor reads off-centre and the assembly is rejected even though every single dimension is in tolerance. Concentricity is therefore the callout that decides the die, the gauge and the price.

Where concentricity comes from

It comes from the tool: punch and die alignment, guide clearance, and whether the part is formed in one hit or several. Where it must be very tight, the last operation is often machining rather than forming, because a machined bore can be centred on a datum that was created after drawing.

How to write the callout

Name the datum feature, define the tolerance zone, and state the measurement method - a CMM report is the usual evidence. Avoid stacking concentricity on top of a general tolerance: it is a relationship between features, not a dimension on one of them.

Grade, wall thickness and tolerance are confirmed against the customer drawing. Batch heat treatment, slow wire cutting, passivation, electropolishing, plating, phosphating and coating are placed with qualified external processors and disclosed on the inspection plan. The quality system is ISO 9001:2015 with controls aligned to IATF 16949 requirements.

Written by the Balford engineering team, Zhuji, Zhejiang, China. Last updated 21 September 2026.