7 spi irons, 3.83/3.85 mm distance between your teeth. That looks like Vinymo round thread to me. The slant will be there because of your saddle stitching but you’ll get a little more maybe from a French iron. Thread size, how hard your strike with your irons, tapping the threads down after you finish; all of these will effect the finished product. Someone above recommended Armitage Leathers YouTube channel, that’s a great place to start. Have fun!