Screw machined from solid prism - has head of same cross=section as original base and has washer force fitted below it

摘要

The screw is machined from either a triangular, square or pentagonal bar and has a head (2) of that shape. The screw is machined in the lower part of the solid bar and has a collar (31) of a larger diameter than the screw machined below the head. A washer (7) is forced over the collar below the head. The screw requires a special shaped spanner to turn it. A screw machined in this way minimises the amount of wastage of the base material.