GURPSよろず

Skills and Size Modifiers　F137P
Making arms or armor for members of larger or smaller races is a challenge for an armorer; the fit, balance, and other qualities need adjustment in ways that may not be obvious. Effective Armoury skill is at -1 per point of difference in SM between the two races. A man making a sword for a halfling (SM -2) would roll against Armoury-2, and so would a halfling making a sword for a man! The same applies to various other crafts and design skills: Architecture, Sewing, and even Cooking. Experience in working for such customers can overcome this difficulty; treat each new SM as a new Familiarity.
Using weapons designed for members of larger or smaller races is also harder: -2 to weapons skill per point of difference in SM. If the penalty is -10 or greater, the weapon is simply not usable. This is in addition to any problems with required ST. The same applies to using tools or other gear. These penalties reflect sheer difference in physical size and cannot be bought off (except by changing size).