The 9" x 11" is the most popular size and is made for 8" x 10" cassettes. 
The 11" x 13" grid is designed to be used with 10" x 12" cassettes.

Specifications:
6:1 ratio
Focal distance 26-32"
103 lines per inch
The short S.I.D. of 26-32" makes it more effective with portable x-ray machines.

Dr. Redden has found that this grid greatly enhances the detail and contrast with venograms and all navicular studies.

A must have for equine podiatrists!