CHMOD files in subdirectories

What command do I use if I want to change the permissions on all files in sub-directories, but not the sub-directories themselves?

Example:
maindir
- subdir1
-- file1
-- file2
-- file3
- subdir2
-- file1
-- file2
-- file3
- subdir3
-- file1
-- file2
-- file3

I want to change only the permissions on the files in the sub-directories.

I tried chmod -R 644 *.* , it didn't work.

 

^

chmod -R will change all files and directory

 

Try chmod -R 644 MainDirectoryname

 

Someone showed me the answer here.

 

Thanks for your compliment. I make sure the person-in-charge gets your message.