After adjusting, perform the described in the Kingtex manual:
: Available in 4 and 5 thread variants (e.g., SH-6004, SH-6005). Differential Ratio : Adjustable between 0.7 and 2.0. Max Sewing Thickness : Approximately 10mm to 12mm. Essential Spare Parts Commonly replaced parts for these machines include: Kingtex SH 6000 Series Doc 153 | PDF - Scribd
: Typically up to 12mm or 17mm depending on the configuration.
: High-quality metal and ABS components provide the durability required for 24/7 industrial environments.