I’m new here, and I couldn’t find this answer on the web site or forum.

What do the digits/letters of the shaft MPF rating mean? I found info on how head MPF is determined, but nothing about shafts. It seems the first digit relates to flex, but I’m not sure after that

The reason for my question is to get a feel for what is nearly the same. For example, is 3D3S similar to 3D3M? What about 3B3M? Etc.

Thanks for your help.