I have an old book that has quite a bit about this, Making and Using the Fly and Leader
by Paul H. Young, 1933
You wouldn't know it unless told , but when you hear reference to Cat Gut, the cat is short for caterpillar.
The gut strands were normally 12 - 15 inches but longer strands of 20+" were available and very expensive. Of course there was huge advantage of a dry fly tippet of this length
"Drawn" gut was drawn through a diamond die to provide a consistent diameter.