360.10—Amounts which may be purchased.
         The amount of savings bonds of Series I which may be purchased and held, in the name of any one person in any one calendar year, is computed according to the provisions of  § 360.11 and is limited as follows:
    
    
    
        
        (b) 
         Special limitation, $4,000 (par value) multiplied by the highest number of employees participating in an eligible employee plan, as defined in  § 360.13, at any time during the calendar year in which the bonds are issued.