is there anyway to change the default dimention value for those custom parts?
then we can use it dirrrectly and do not have to change it every time.
You need to edit the “CustomParts Imperial Catalog.pcat” and/or “CustomParts Metric Catalog.pcat” that are located in the folder "C:\AutoCAD Plant 3D 2013 Content\CPak Common".
Once you have done that you need to update the specs that are stored here (CustomParts Imperial.pspx and/or CustomParts Metric.pspx):
C:\AutoCAD Plant 3D 2013 Content\CPak Common\CustomPartsSpecs.
I hope this helps.