Disclosed is a device comprising a base part and a top part that can be joined to the base part via a releasable locking connection. A very accurate and mechanically robust determination of surface geometric data, e. The method also relates to a method for producing a spark plug for an internal combustion engine, the spark plug having at least two electrodes. Rotation of the spool draws in a tensile member passing through the commissure posts, drawing the commissure posts inward toward the spool.