Is FIX a solid hold in .asm

Fix constraint will "freeze" the position and orientation of the model relative to a reference coordinate system.  Note that if the reference coordinate system is not specified in the UI (default action), then the default coordinate system of the component's parent assembly is used as the reference.

So if the reference coordinate system moves then the component fixed to it will move along with it.

Also note if you fix a subassembly that has unconstrained components, then those sub-components will still be draggable in the top level assembly.

Default constraint will align the model's default coordinate system with the parent assembly's default coordinate system.

Csys constraint will align a coordinate system in the model with the reference coordinate system.

Fix is a great tool in the tool box. I like to use it when I need to "float" something in to my assy that may be not be ready for constraints but I need to account for it and and for it to be adjustable by dimension. If you "edit" a fix component, you can see and modify the 6 degrees of freedom, x,y,z and the 3 angles. 

Sometimes you just need something approximately located, temporarily and just grabbing moving it, so just leaving it unconstrained is okay (temporaily) but sometimes you something located a little more firmly and fully adjustable but without respect to other components, so fix works like a charm.

Fix can be left as a permanent constraint but in my use cases, its usually just a tool I use to help as I work on my design. I wouldn't suggest leaving a packaged component permanently unconstrained since they can be too easily moved. 

Its a tool you can use.

Default constrained aligns the default coord system of the component being assembled directly on top of the default coord sys of the assy. I use this for the first component of an assembly often.

Csys constraint is "any" selected csys in the component coincident to "any" selected csys in the assembly. This is handy for applications like "in body" design or skeleton controlled placement. 

All are good tools that can help you get the job done. 

Hi @Yogesh.T,

I wanted to see if you got the help you needed.

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Thanks,
Anurag