Tap and die sets
Gary Stretton tests five affordable sets to restore old threads or cut new ones
We test five affordable sets to restore old threads or cut new ones
THREAD quality is a matter of time and preservation – the better the thread the less time assembling or disassembling and, crucially, the better the preservation of potentially expensive components.
If you’ve ever struggled to remove a seized fitting in an emergency without destroying it because it has to be refitted, you’ll appreciate being able to make good a poor thread before reassembly. For instance unique suspension bolts you hadn’t expected to remove and Series/defender body panels’ captive nuts. Exposed corroded threads, seized fittings with corroded threads or freshly coated threads blocked with galv or paint will undermine and potentially weaken a fitting to the point where it could break, cross thread or seize. One way to avoid this is the use of taps and dies to restore thread integrity. With a few minutes practise, you can ensure your fittings will glide on and off as required.
For this test, we’ve focused on metric thread sets only, although some sets may include other popular threads. If you don’t possess a comprehensive range of drill bit sizes beyond the standard diameters, a tap and die set which includes the matched size drill bits will get you started out of the box, and will ensure accuracy for your threads and lessen the likelihood of a tap snapping in situ. Matched drill sizes are mostly in between sizes, such as 6.8 mm for an M8 thread.
Dies are available as split or solid types. Solid dies are best suited to re-cutting existing threads, while split types allow a degree of adjustment when creating new threads. Die holders feature in differing sizes, with or without a guide tool for keeping the die level on a new piece of rod or bar.
Taps in these sets are mostly tapered, ensuring they can start cutting a new thread more easily. Plug taps are easier to use when cleaning up an existing thread and can cut further into recessed holes if necessary. Tap wrenches also differ in size but generally feature the same mechanism for clamping the square end of a tap. For smaller taps, a T-type tap wrench is useful for use in confined spaces.
Additions, such as a thread pitch gauge, will prove useful and eliminate the possibility of incorrectly identifying a thread pitch.