regex meter string : I want to use regex in Python to obtain the three following types of product dimensions from a string (notice the spaces). 

1) 20x20mm
2) 20 x 20 mm
3) 20x20 mm

These are all contained in the middle of strings, representing sizes or products. 
I figured I could find these product dimensions by using Regex to find the 'x' or 'mm', as these are the constant strings. I would like to obtain an output that just gives me the product dimensions. 

Could anyone help me out with this? 

An example string would be this:

"XY SmallProduct with BIZ/10351, transparent, 75x150mm, Inh. 12"

Thanks in advance!