Types of Bolts and Their Uses (with Pictures)
Every bolt family side by side with pictures — head styles, thread behavior, and what each one fastens, from carriage bolts to timber bolts.
Hex Bolt
Six-sided head, wrench-driven — the universal bolt.
Best for: Machinery, construction, general assembly
Carriage Bolt
Smooth dome head with a square neck that locks in wood.
Best for: Decks, fences, furniture
Socket Head Cap Screw
Allen-driven cylinder head for precision fits.
Best for: Machinery, engines, robotics
Shoulder Bolt
A precision unthreaded shoulder that doubles as a pivot shaft.
Best for: Pulleys, linkages, moving joints
Flange Bolt
A built-in washer flange spreads load and skips the washer.
Best for: Automotive, machinery frames
Stove Bolt
A small round-head machine bolt for sheet metal.
Best for: Appliances, electrical boxes, brackets
Plow Bolt
A flat countersunk head for soil-contact steel.
Best for: Plows, graders, earthmoving blades
Square Head Bolt
Old-school square head with maximum wrench grip.
Best for: Restoration, timber framing, railroads
Timber Bolt
A long small-diameter bolt for landscape timbers.
Best for: Retaining walls, timber stairs
Through Bolt
Passes fully through and clamps with a nut — the strongest wood joint.
Best for: Beams, ledgers, post bases
How to Choose
Also in the toolbox
- Deep socket set (SAE and metric) — seats every hex head above
- 1/2-in drive torque wrench — structural bolts want real torque values
FAQ
What is the difference between a bolt and a screw?
A bolt passes through unthreaded holes and clamps with a nut; a screw cuts or follows threads in the material itself. If it needs a nut on the far side, it is a bolt — with the confusing exception of lag bolts, which are really giant screws.
What do the markings on a bolt head mean?
Radial lines mark SAE grade: no lines is Grade 2, three lines is Grade 5, six lines is Grade 8. Metric bolts stamp numbers instead — 8.8 and 10.9 are the common structural grades. More marks, more strength.
Why do bolts need washers?
Washers spread the clamp load so the head and nut do not crush into the material — critical in wood — and protect finishes. Always use them in wood; in steel they are good practice that also evens out the joint.