A portable articulated arm coordinate measurement machine is provided. The coordinate measurement machine includes a manually positionable articulated arm having opposed first and second ends. The articulated arm includes a plurality of arm segments, each including encoder configured to produce a signal corresponding to an angle of rotation. A base section is connected to the second end. A measurement probe is connected to the first end. The measurement probe receives an externally mounted sensor having an attachment ring, the measurement probe having an alignment surface and external threading. A retaining ring having internal threading is threadably receives the external threading; the retaining ring further couples the attachment ring to the surface. An electrical circuit is configured to receive the signal and to provide data corresponding to a coordinate of the externally mounted sensor, the data based at least in part on the signal.