Developed by Charles Greenfield and patented in 1874, the aptly-named greenfield tap wrench is used to create a whole new set of screw threads or to enlarge pre-existing ones. Its usefulness has stood the test of time.
The head of a tap wrench is attached to the handle at a swivel joint, which allows it to rotate with ease. The head is cylindrical in shape and has a square hole in its center. This is where the tap is inserted, and when turned it will create the desired thread. This combination of parts makes for an effective device that quickly and accurately produces new threads.
Crafted from wood or metal/plastic, the handle of a tap wrench is usually 12 inches (30 cm) in length, although some differently-sized models may sport a handle of differing proportions.
To accommodate a range of tap diameters, Greenfield tap wrenches are offered in the four most popular sizes – 0, 1, 2, and 3. A size 0 taps measures 0.25 inches (or 6.35 mm), while size 1 equates to a 0.375 inch (or 9.5 mm) diameter. Similarly, a size 2 and 3 fit taps with 0.5 inch (12.7 mm) and 0.625 inch (15.9 mm) diameters.
Tap wrenches prove their worth when starting threads in empty holes or bolstering existing ones. It’s also useful to have one nearby if there is a need to cut out threading that’s gone bad or become blocked.
To utilize a greenfield tap wrench, first slot the tap into the square opening on top of the wrench. Then twist the grip in the necessary direction to create a new thread. If you have a right-hand tap, twist clockwise, and counterclockwise for a left-hand tap.
Turning the tap, a thread of a new form is carved into the aperture. The size of the thread is established by the tap’s length – supplying a justification for using diverse taps for distinct occupations. If tapping a hole for attaching a screw, then a shorter tap is utilized to compare with a longer tap when enlarging an existing thread in a conduit.
After the tap has brought the thread to its intended depth, it is extracted from the opening and checked for quality. If requirements are not satisfied, the activity can be performed again.
Every machinist and engineer knows that a Greenfield tap wrench is an absolute must-have for their toolkit. From fashioning brand new threads to refining existing ones or even clearing clogged threads, this durable and hardworking tool can do it all.
Although they are often associated with metalwork projects, greenfield tap wrenches can also find a place in woodworking or plastic-based jobs. By providing a bit of TLC and keeping up on routine maintenance checks, these wrenches can become long-term fixtures in one’s toolkit.