Question

the component shown circled in the image here: designed for locking a dimension by preventing motion of the spindle provides smooth uniform pressure independent of feel permits measurements in narrow slots and tight places provides a breaking away at a consistent gram force insuring repeatability

Explanation:

Based on typical knowledge of measurement - related components, the part circled is often a locking device for a measuring instrument (such as a micrometer). Its main function is to lock a dimension by preventing the motion of the spindle.

Answer:

designed for locking a dimension by preventing motion of the spindle