L1A1 barrels are timed utilizing a washer between the barrel shoulder and receiver. 1.00″ ID and 1.20″ OD.
Sizes 1-8 are normal factory range. Other sizes are custom made from low carbon steel for abnormal barrel timing.
To make sizes larger than .060″, add a .002″+ timing shim from the fal barrel group section.
Current DSA L1A1 Australian pattern receivers usually require a .060″ AND a .002″ OR .003″