Garyak

Those are what you’d call distressed leather. It can be anything, bovine, swine, etc. it’s done in the process off tanning.

https://drive.google.com/file/d/1BInD1kgMM1GeHjNmvX9pL5AuArThjFLI/view? Uploaded file: 14218b_ch9_10.pdf

Google search the U.S. Air Force safety keepermans training manual. Skip the oxygen canisters section on to the sewing machine section. Here you will learn in the simplest of terms how to diagnose, and repair anything that could pop up on any sewing machine in the world. Even has a troubleshooting section… find your issue, right next to it is your solution. Any problems that can happen are caused by very specific things. Like skipped stitches or not grabbing the bobbin thread, there’s only a couple things that cause that, needle set incorrectly, wrong needle, presser foot isn’t keeping the material in contact with the bed, add presser foot pressure. I see people saying timing every time a stitch is skipped. With that PDF you will never ask another question online again. Covers 4 of the most common machines, 2 of each kind, oscillating shuttle (31-15), and rotary hook (singer 145 juki 158). Only two that matter to us anyway. You won’t be disappointed.

Above the foot, there should be a stitch length screw/clamp. It slides up and down the feed bar. All the way down to full feed, up for zero.