Ron,  

We have found these same washers in association with mining and utility pole 
sites in Nevada.  The washers were patented by Charles G. Ette, St. Louis, 
Missouri. The first was listed on 10 May 1904, Patent No. 759,599 (utility), for 
a term of 17 years, (United States Patent Office 1904:110(2)484), and the 
second on 29 October 1907, Patent No. 869,235 (utility), also for a term of 17 
years (USPO 1907:130(4)2385).  This information can also be retrieved 
through the United States Patent and Trademark Office website.  Utility is 
noted because that number requires no letter preceding the patent number.  I 
believe the "MALL" stands for "malleable iron or other malleable material," as 
noted by Ette in his second patent.  The first patent describes the various 
uses of the washer on tie-rods employed in structures that have heavy 
strains, such as bridges and roof structures, as well as mining equipment and 
the like.  The washers apparently came in more than one size or strength.  
The utility pole isolate had two of these washers, one labeled with "5/8 10" 
and the other "...3/4 10."

Niki Kimball