This is a set of four Plumbers and Steam Fitters guide books by Theodore Audel & Company printed in 1947. The first book outlines the mathematics, physics, materials, tools and lead work. Book #2 outlines water supply, drainage, rough work and tests. Book #3 outlines pipe fitting, heating, ventilation and air conditioning. Book #4 outlines gas, sheet metal work, welding and motors. Each small book measures 5" by 6.75" and is just 1" thick. All are in near mint condition with exception to book one. The inner binding of the front cover has separated and the first page is loose.