Youtube video - "Solidworks motion tutorial cam and spring animation" 22:42 shows a spring that is compressed or extended by manipulating endpoint of center line of spring. I cannot move spring at all!!! Can someone tell me what I'm doing wrong.

In the Youtube video "Solidworks motion tutorial cam and spring animation" 22:42 / 33:16 The designer is able to snap onto top of endpoint of center line and compress or expand spring by making line longer or shorter. I cannot manipulate spring length at all this way. The line will not change length. What am I doing wrong??

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