"Andy Burns" wrote in message
...
Stephen wrote:

Why is it that metal back boxes come in 25mm, 35mm, and 47mm sizes but
surface mount pattress boxes only come in 25mm and 47mm sizes?

search and ye shall find


http://www.alertelectrical.com/Wirin...Box-CMA083.asp

You also have more choice at
http://www.electricalshop.net/acatal...ttresses_.html so you're
not stuck for depth.