Remember too that the holding power of the screw is no greater than the strength of the material into which it is driven. Soft woods, thin laminates, and thin metals cannot carry much of a load. Conventional wood screws are superior for fastening wood joinerwork, but they should never be used to fasten into fiberglass laminates. Bolts For heavier loads, for pulling two surfaces together, and for fastenings that may be repetitively tightened and loosened, bolts are the answer. These functions are in direct contrast to those that screws perform best.
Machine screws come with flat, round, and oval heads, all slotted for use with a screwdriver.
All are capable of taking a variety of washers underneath. Machine screws axe often used in heavier metal without a nut by drilling and tapping the hole. Nuts are intended to be tightened against a washer. The washer not only spreads the load on the lower surface of the material being bolted, but prevents the nut from cutting into that surface. A good sealant should always be used with through-bolts in a hull or deck, as the bolt holes provide passageways for water.