6933⅓ yards per oz.
In the Manchester silk scale the yards per ounce of a 4 dram silk may be found by multiplying 1,000, the yards in a hank, by 16, the drams in an ounce, and dividing by the number of drams which the hank weighs, viz. 4; thus—
1000 × 164 = 4000 yards per oz.
Twofold Yarns in cotton, worsted, and linen are numbered according to the count of the single yarn, with the number of folds put before it. Thus a 2-40’s yarn means that the yarn is composed of two threads of 40’s single, making a twofold yarn of 20 hanks to the pound.
In spun silk the yarns are nearly always two or more fold, and the number of the yarn always indicates the number of hanks in 1 lb. The number of folds is usually written after the hanks per pound. Thus, 40’s-2 spun silk indicates that the yarn is 40 hanks to the pound, made up of two threads of 80’s single.
It sometimes occurs in fancy yarns that threads of unequal thickness are twisted together. If a 60’s thread and a 40’s thread are twisted together, the count of the doubled thread will not be the same as if two threads of 50 hanks to the pound, but will be something less than this.
It is obvious that when the two threads are twisted together the weight of a hank of the doubled thread will be 1/60 + 1/40 of a pound, and by adding these fractions together the counts of the twofold yarn may be obtained. Thus—
140 + 160 = 3 + 2120 = 5120 = 24’s counts.
Another method of obtaining the same result is to multiply the two numbers together, and add them together, and divide one result by the other. Thus—
60