This M1style helmet shell I believe that I have now identified as being a Danish M48 helmet shell by Diaward Steel Works of Hong Kong for the Danish Civil Defence. The entire helmet shell is magnetic but this helmet supposedly passed all of the same tests that the original US M1 helmet passed before being purchased by Denmark
. The colour does appear to be a dark, drab khaki rather than grey as may be expected for Danish Civil Defence. The number 56210 on the rear rim would indicate that it is one of last of the the 60,000 for the Danish Civil Defence.