Description:<br>12.9 class screws as the top of the screw， with high hardness and tensile strength， Rockwell hardness (HRC) up to between 39 and 44， the tensile strength of up to 1220N \/ mm2. mainly used to the textile， hydraulic， injection molding and mechanical industry.<br>Specifications:Type: flat endColor:blackMaterial: Carbon steelCategory: hex socket Fastening screwPackage size:11x6.6x2.3cmSize(mm):<br>          Diameter       Inner diameter       Length       Quantity           2        1       3       20           2        1       4       20           2       1       6       20           3       2       4       20           3       2       6       20           4       3       5       20           5       4       6       20           6       4       5       20           6       4       10       20           7.5       5       8       20   <br>Features:Tight structure， great stabilityWith high hardness and tensile strengthWithin the hexagonal bolts 12.9 cyanide blackened surface， it  is rust-proof<br>Operation method :1. Must be vertical to the spools of thread are screwed， do not tilt;2.In the screwing process， rotation force must be uniform， tighteningtorque can not be more than safe torque;3.As much as possible using torque wrench or socket wrench， avoidthe use of movable wrench or electric wrench;4.Avoid use under the condition of high temperature， use don't fastrotation， avoid rapid temperature rise and cause the lock.<br>Package included:200 x Flat Head Hex Socket Screw