01 Outer hex screws
The thread on the outer hexagon screw is generally fine tooth ordinary thread, and the outer hexagon screw with ordinary thread around the ring tooth has good self-pin performance, mainly used for thin-walled parts or occasions under impact, vibration or alternating load.
Generally, the outer hexagonal screws are made of partial threads, and the full-thread outer hexagonal screws are mainly used for the outer hexagonal screws with short nominal length and the occasions requiring longer threads. External hexagon screws with holes are used when external hexagon screws are required to lock. The outer hexagon screw with reamed holes can accurately fix the phase to position of the connected parts. And can be subjected to shear and extrusion caused by mold forces.
The advantage of the outer hexagon is that the pre-loaded contact area is large, you can use a large pre-loaded force, generally used in large equipment, the price is lower than the inner hexagon, the disadvantage is that the space is large, can not be used in the countersink hole.
02 Hex Socket screws
Hex socket screws are often used in machinery, mainly easy to tighten, disassemble, not easy to slip and other advantages. An Allen wrench is usually a 90 degree bend. One end is long and the other is short. When using the short side to screw, holding the long side can save a lot of force and tighten the screw better. The long end has a round head (hexagonal cylinder similar to a sphere) and a flat head, and the round head can be easily inclined to disassemble and install some parts that are not convenient to lower the wrench.
The manufacturing cost of the outer hexagon is much lower than the inner hexagon, and its advantage is that the screw head (wrench stress position) is thinner than the inner hexagon, and some places are not the inner hexagon can be replaced. In addition, the cost is low, the dynamic strength is small, and the precision requirements are low.
The advantage of the hex is that it occupies a small space, can be used as a countersink, generally used in small equipment, the disadvantage is that the pre-tightening contact area is small and can not be used with too large pre-tightening force, the price is more expensive, and there is no full thread over a certain length.