M8 x 18 mm - Flat Head. M8 x 17.5 mm - Small Head. M10 x 21 mm - Flat Head. M4 x 11 mm - Flat Head. Flat head provides a good bearing area for application surface and for bolted-on part Hexagonal shank used in conjunction with a hexagon hole to give maximum resistance to applied torque or unscrewing torque.
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