Home / United States / World War I / Collar Disks / Battery M 20th Field Artillery Collar Disk Battery M 20th Field Artillery Collar Disk$25.00 WWI Battery M 20th Field Artillery Collar Disk. Shows some wear on its face, screw back – has its nut. Battery M 20th Field Artillery Collar Disk quantity Add to cart Item Number: 793 Category: Collar Disks