I am unsure whether the correct size of item was received?

The easiest way to confirm whether it is, for instance, 40mm watches, is to measure the width of the strap.

We offer different sizes of the straps such as 14 mm, 16mm, 18mm, and 20mm, those fit accordingly with the 28 mm, 32mm, 36mm, and 40mm/42mm watch heads, and they cannot be interchanged between each other.

Therefore, if your strap width is 20mm, then your watch is confirmed to be 40mm. If strap width is 18mm, you have a 36mm watch, a 16mm width strap fits the 32mm watch, while a 14mm width strap fits the 28 mm watch.