In Britain and USA, these numbers are called 'counts' when measuring cotton yarn. See e.g. 

 Wikipedia, 'units of textile measurement', or 

 Thomas Woodhouse, *Yarn Counts and Calculations* (London, 1921), available in 

https://www.cs.arizona.edu/patterns/weaving/books/wt_yarn.pdf

 Any web search will turn up other articles. 

 Avner Offer

=======================================================
 From Avner Offer, Chichele Professor Emeritus of Economic History, University of Oxford
     All Souls College, High St., Oxford OX1 4AL, tel. +44 (0)7551960880
    email: [log in to unmask]
    personal website:
    http://sites.google.com/site/avoffer/avneroffer
Recently published: Burn Mark: A Photographic Memoir of the Six Day War. See www.avneroffer.net
________________________________________
From: Societies for the History of Economics [[log in to unmask]] on behalf of James Henderson [[log in to unmask]]
Sent: 06 August 2015 18:49
To: [log in to unmask]
Subject: [SHOE] Measuring cotton yarn at Manchester

    I am researching the debates over the Ten Hours Bill in 1844.  One of the disputants  observed 5 mills, spinning

"No. 14, 15, 30, 38, and 40 yarn"

These numbers are calculated by measuring the length per unit of weight of the cotton spun.  I can't find what unit of length and what unit of weight was employed (the larger the number. the finer the yarn). Any ideas?

James P. Henderson
Senior Research Professor of Economics
Valparaiso University
Valparaiso, IN 46383