I don't think they are fiber-glass, but there is an older style - and  
heavier - milk crate which is about 1/4 inch deeper than the normal  
plastic ones.
        That means they can be stacked up without any pressure on the  
records stored below - not true of those commonly found these days.
Mine were made by Piper Industries Inc. and do have a fiber-ish  
appearance, and typically pink.
      However, you should note the printed caveat "Use by other than  
registered owner - prohibited by law."
  Oh, for the Good-Old-Days when milk-crates were milk-crates !
.
On Mar 12, 2010, at 11:14 PM, Steven C. Barr wrote:

> I have used "milk boxes" for about 40 years, to store my "half-vast"
> 78rpm archive! Each one holds about 120 (or more...I have MANY
> of the old Fiberglas versions!) A full crate weighs 60-65 lbs. (which
> I can still lift...so far...?!). My only problem is trying to find  
> "unclaimed" (I don't take them from grocery stores or dairies!)
> milk boxes, as fast as I purchase more 78's...?!
>
> Steven C. Barr
>