M4 x 0.70mm Pitch M5 x 0.80mm Pitch M6 x 1.0mm Pitch M8 x 1.25mm Pitch M10 x 1.50mm Pitch M12 x 1.75mm Pitch M16 x 2.00mm Pitch. Serrations displace material and create a locking feature which is resistant to vibration.
eBay