# Chain Action [GstarCAD 2017](Help%20System/GSTARCAD/2017/Index.md) → [What's new](Help%20System/GSTARCAD/2017/What's%20new/(What's%20new).md) → [Additional Pages](Help%20System/GSTARCAD/2017/What's%20new/Additional%20Pages/(Additional%20Pages).md) <!-- help-structure:notice --> > **Source status:** This source topic has 5 recorded inherited issue(s). [Source issue details](../../Source%20Issues.md). <!-- /help-structure:notice --> > If you want to realize a symmetric stretch without changing the keyway center and the length of smaller diameter shaft changes with the stretch at the same time, how can you realize that? > > 1\. Add stretch for Step Shaft > > Add stretch parameter and action for step shaft as the following picture shows. Thereinto, the bolded objects indicate the operation object of action. > >  > > Because the follow-up operation will not stretch the step shaft by grips of this linear parameter, the grip’s number of the linear parameter can be modified to “0”. > > 2.Add linear parameter for keyways > > Set the base point position of the line parameter as “Center” in order to realize the symmetric stretch function. > >  > > 3.Add the stretch rightwards action for the keyway > >  > > 4.Realize chain action > > Select the “Distance” linear parameter and modify the chain action of prosperity from “NO” to “Yes” as the following picture shows. > >  > > Add the Stretch Leftwards action for keyway as the following picture shows. Special Note: Do elect “Distance” for the linear parameter to stretch leftwards the operation objects set. This is a necessary procedure of the chain operation. > >  > > 5.Test Dynamic Block > > After dragging the left grip, not only the keyway will stretch bi-directionally and symmetrically but also the smaller diameter shaft of the step shaft will stretch automatically. This is a chain action. > >  > > The realization of a chain action has two important procedures: First, modify the property value of the parameter that need to happen as linkage and modify the property of “chain action” from “NO” to “YES”. Second, elect the parameter of objects that are elected to linkage action to set. --- Gstarsoft Co.,Ltd