How To Choose The Right Bolt

Wrench, nuts and bolts

There are a number of different bolts and nuts on the market, each designed for specific applications.

Common Bolt Types

  • Carriage Bolts - Traditionally designed for use in woodworking. The bolt features a rounded head minus a slot, as well as a square shoulder that fits in the sunken hole to stop it from turning when the nut is being tightened. Use this bolt when you don't want a protruding head.
  • Stove Bolts - General utility fasteners. Their heads are slotted and can be oval, flat, or round. Their entire lengths are threaded.
  • Machine or Hex Bolts - Also for general utility. They have 6-sided heads and their lengths can be partly or wholly threaded. They are used with ratchets or wrenches.
  • All-Thread Bolts or Threaded Rods - Helpful when you require additional length, up to 3 feet. These do not have heads and can be cut to size using a hacksaw blade. Threaded rods are secured using bolts fastened on either end.
  • J-bolts, U-bolts, and eyebolts - Used as hooks or as supports. These also do not have heads.

Save Old Bolts

Finding an exact bolt replacement will be easier if you bring along the old bolt. Remember that bolts with similar dimensions can still have different thread pitches.

Bolt Notations

If you lose an old bolt, you may have to guess which new one you need. Preempt this by learning to read the numerical notations used on different bolts. Bolts generally have their pitches described as fine, medium or coarse.

The same pitches are also numerically described using both a fraction and a whole number. The fraction, say ¼, is a quarter-inch and the bolt’s diameter. The whole numbers, which represent the pitch, can either be 12, 24 or 36. These correspond to the fine, medium and coarse grades respectively.

Remember that bolts in non-American cars may use metric numbers.

Different Materials

Stainless steel bolts can be expensive, but they won’t get corroded. Grade 8 bolts are hardened for maximum strength, so you can use them for installations that require absolute safety. Grade 5 bolts are less strong and should be used indoors, like in furniture.

Galvanized bolts are similar to Grade 5s, but are coated in zinc for corrosion resistance. These are a good alternative to stainless steel bolts.