Hex bolts have a chamfered point to aid insertion into a tapped hole or nut. Length is measured from under the head.
Nylon 6/6 is a general purpose thermoplastic with outstanding resistance to organic chemicals, acids and alkalis. Nylon wears well against other surfaces; it is readily machinable and may be milled, turned and cut with conventional machine tools. It does exhibit some dimensional swelling in wet applications which should be taken into account with its use. Tensile strength of this material is 12,000 psi (pounds per square inch).
Hex head fasteners can be driven with simple wrenches, and require minimal clearance above the fastener because they can be driven or loosened from the side.
A threaded fastener's size name includes information about the major external diameter (in millimeters), followed by the thread pitch (millimeters per thread), which indicates if it is coarse or fine.