How to describe a product?

[Mark_000]

Hi,
In terms of describing a product, could you please help me to check a few words and sentences? Thanks a lot.

1. outline or perimeter
Assuming a diameter of a circular components is 7mm and this components is very simple. I want to point this outside 7mm line.
Eg: The adhesive tape should be assembly to the back surface of this components. Therefore, it should be at least 0.3mm smaller than the outline/perimeter of the product for avoiding any overflow issue. (I'd use perimeter, right?)

2. shape or geometry
Eg: The shape/geometry of this product is similar to a rectangle. (I think both are acceptable, right?)

3. The dimension for this rectangle is 3cm*2cm. (can 3cm*2cm be replaced with 3cm by 2cm?)