Multiple Category Templates

Hi,

I’ve customised the template for one of my categories by creating a PHP file called category-6.php and this works fine. This category now looks different to other categories.

But lets say I make a sub category of this (called cat 7) and I want it to use the same template as its parent. Do I have to duplicate category6.php and rename it 7, or is there a way to tell all sub categories to follow its parents template?

Or a way to simply say category-x.php is to be used on category x, y and z?

I don’t particularly want to just duplicate and rename my files as this means if I need to make one change I have to change a lot of templates.

Thanks in advance for any help thrown my way!
Matt