The types of bolts used in mechanical engineering are incredibly diverse, each designed to solve a specific technical problem. A common mistake made by many new mechanics is using the wrong type of bolt, causing difficulties in installation and maintenance and reducing the accuracy of the machinery. The two most common types that are often confused are external hexagon bolts and internal hexagon bolts.
External Hexagon Bolts
Features: The most common type of bolt, with an external hexagon head. Requires a wrench or spanner to tighten.
Advantages: Inexpensive, widely available, withstands high tightening force, easily found in any hardware store.
Applications: Used for bolts and screws in heavy machinery assembly, joints that don't require extremely high precision, and most importantly, where there's "space" for wrench operation. Examples: assembling machine frames and bases.
Mistake in use: Trying to use it in a tight machine compartment. You won't have space to rotate the wrench, making tightening the bolt a torture.
Recessed Hexagon Bolts
Features: The bolt head is cylindrical with a recessed hexagonal socket. A hex key is required for tightening.
Advantages: Extremely compact. Can be tightened in extremely tight spaces where a wrench cannot reach. Very high and precise tightening force (due to the snug fit of the hex key). High aesthetic appeal, does not protrude.
Applications: Required for use in precision machine parts, molds, jigs, and anywhere with limited space.
Mistake in use:
Using it in locations subject to strong vibrations: Recessed hex key bolts tend to loosen themselves when vibrating (if not using spring washers or threadlocker).
Using the wrong hex key: Using a loose or incorrect hex key (metric/inch system) will strip the bolt head. Removal will then be impossible.
Countersunk Hexagon Flat Head Bolt
Mistake: This is a special type of bolt with a beveled head. It's designed to be flush with the surface of the machine part. Many people use it to fasten on a flat surface.
Consequence: The entire tightening force is concentrated on the beveled edge, damaging the surface of the part and resulting in unstable clamping force.
Note: Only use this type when the hole has been pre-beveled (cut off the edge).
Using the correct type of bolt for the correct position is a fundamental requirement of engineering. External hexagon bolts are for areas with ample space, countersunk hexagon bolts are for confined spaces, and beveled head bolts are for areas requiring flush mounting. Confusing them not only makes assembly difficult but also directly affects the durability and safety of the machinery.
