[Problem with area of the object]

Thanks to your advices I solved the problem ,I had to ungroup the models and then to group them again

to cancel these lines

thanks guys

[Problem with area of the object]

Good day to everyone ,i have this problem, when I load a model in cura I often have these grey thin lines that

define the area of the object to print with the only problem that the area is the one of the yellow object itself,

i want to print only the yellow object but the printer cosider all the space between thin lines and the object as an area to print ,so I have problems

to give dimensions to the object!How can I delete the grey thin lines so the printer consider only the yellow object as an area to print?