original item: common part in spare parts wallet for lock spacing
Included 1 x No. 1 Vickers Lock Headspacing Washers, No. 1 .003 thickness
From “Handbook of the Vickers Machine Gun”
Test lock for excessive head space,
a—Remove recoil spring and box.
b—Remove lock and place washer over crosshead.
c—Replace lock; pull roller handle to the rear.
d—Place dummy on carrier opposite firing pin hole. (Use dummy made from live cartridge that is not distorted; on the range live cartridge may be used).
e—Raise carrier and hold it in its highest position.
f—See that barrel is forward,
g—Push roller handle forward slowly,
h—The roller handle should stop short of the dead stop and a slight tap should be necessary to force it down. (If the roller handle goes onto the dead stop freely, another washer is needed).
i—If a slight check is felt in carrying out (h), the washer is not needed.
• With gun properly assembled pull roller handle to rear until ears of carrier drop into notches in side cams. Place thumb against the rear of the roller handle and fingers on the front near the lower end of roller handle; move barrel and recoil plates backward and forward several times to see that the recoiling parts function properly.