Thread and needle sizes

[Furiku]

I am reading about people using certain needle sizes and thread sizes for various appications in leather work. I cannot find anywhere, any information about what needle to use with what size thread for any specific use, whther it is for hand sewing or machine sewing. Can anyone please direct me to where I can find this info....?

[DrmCa]

Here's a simple chart published by American and Efird http://www.amefird.com/technical-tools/thread-size/fabric-weight/ and there are many more in the first page of google.

I tend to use A&E threads and mostly go with their chart.