The extent of the pre-drilling depends primarily on the diameter of the screw. Naturally the diameter of the pre-drilling always falls between the core diameter and the nominal diameter of the screw.
Further factors that influence the extent of the pre-drilling:
The sheet thickness
The thicker the sheet we want to drive the screw into, the closer the hole diameter has to approach the nominal diameter of the screw. That is, the thicker the sheet we want to screw the screw into, the larger the bore we have to prepare for it.
The material of the sheet
Harder sheets that are more difficult to form have to be pre-drilled with a larger diameter than easily formable sheet.
The technology of the pre-drilling
If we make the hole not with a drill or a punch, but without cutting, by rolling or pressing, then we have to form a hole of somewhat larger diameter.
In every case let us carry out a trial before we begin mass production!
The table below helps to select the pre-drilling tool of the appropriate size under all circumstances.
If you do not want to pre-drill at all, then choose a bi-metal self-drilling self-tapping screw!
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