For the couching the relative position with a screw. When using mechanical fastening screws into the fixing screw holes in the end to squeeze in another part of the screw on the surface, even if the previous mechanical fixed on the latter part. Slotted and Hexagon socket set screws are used on exposed parts of the head does not allow, square head set screws applied on exposed parts of the nail head allows. Screw tightening force for slotted screws minimum, square head screws maximum, centered hexagonal screws. Cone end screws applies Yu strength small of parts Shang; no pointed cone end screws suitable for pressure tight surface Shang business has concave pit of parts Shang, to increased passed load of capacity; flat end screws (pressure tight surface should is plane) and concave end screws, are applies Yu hardness larger or often adjustment location of parts Shang; long cylindrical end screws applies Yu tube shaped axis (thin-walled pieces Shang, cylindrical end into tube shaped axis of eyelets in the, to passed larger of load, but using Shi due prevent screws pine off of device.