How to Tap for Galvanized Bolts

What You'll Need
Tap and Die
Tap Chart
Tapping Fluid
Safety Gear (Gloves, Goggles, Apron)

When you are working on certain mechanical projects, you may find the need to tap a hole for galvanized bolts. When building something from scratch, or repairing threads that have been damaged, tapping new threads is a much needed skill. A simple tap and die set is relatively inexpensive, but an important part of a mechanic's, or fabricator's, toolbox. For anyone who has ever tapped a hole for the threads of a bolt, you do not have to learn how to do anything new. The procedure for tapping a hole for galvanized bolts is much the same as with any other type of standardized bolt. If you have never had to tap a hole for galvanized bolts or any other, then here is a step by step guide to help you.

Step 1: Reference Tap Chart

To begin tapping a hole for galvanized bolts, you will need to know the actual size of the drill bit that is needed for the bolt you are going to use. For a good rule of thumb, you should use a drill bit that is one size larger than the hole that you need. As you are looking at the drill and tap chart, you will find the size that you need directly across from the final threaded hole size.

Step 2: Set Up Drill

Once you have determined the right size of the drill bit that you will need, set it up in your drill. Make sure to chuck the bit tightly so it does not spin in the drill. 

Step 3: Apply Tap Fluid to Bit

When drilling a hole in metal, there is a tremendous amount of heat that is generated through the friction of the drill bit and the metal pieces. This heat can cause damage to the hole, the bit, and the threads if you try and tap it without the fluid. Apply very liberal amounts of the fluid to the bit before drilling.

Step 4: Drill Hole

Carefully set the drill into position and begin drilling the hole for the threads. Make sure that you hold the drill perfectly perpendicular to the hole so that it is not elongated or misshaped. 

Step 5: Set Up Tap

Use the T-handle and position the appropriate tap into the handle. Coat the tap with fluid again so that it will easily cut through the metal without warping the new threads. 

Step 6: Drill Tap

Place the cutting edge of the tap into the hole and begin turning the T-handle clockwise. This will start the threading process. Make sure to keep the tap perfectly straight and do not force it through. If you feel that there is resistance, back out the tap about a 1/2 turn. This will clean out some of the shavings so you can begin threading again. 

Step 7: Clean Metal Shavings

Once you have finished with the threading of the hole, you must clean out the metal shavings. Use some compressed air to blow away the shavings and debris. Place galvanized bolts in the threaded hole and try it. If it does not work properly, clean out the threads again with the tap.