Definition
A tapered cutting tool used to start cutting internal threads in a hole. The cutting edges are ground at a gradual taper along the first 8 to 10 threads so the tool eases into the work, removing a small amount of material with each thread until full thread depth is reached near the back of the tap.
Plain English
A threading tool with a long, gradual point on it. The point lets the tool start cutting threads gently, going deeper as it screws in, so it's easier to keep straight and less likely to break.
Context Anchor
Seen in aircraft maintenance when a mechanic is making or repairing threaded holes in aircraft parts.
Derivation
From 'taper,' meaning a gradual narrowing to a point, and 'tap,' the general name for a tool that cuts internal threads. The taper refers specifically to the long, gradual lead-in on this style of tap, which distinguishes it from plug taps and bottoming taps.
Why Pilots Care
Mechanics and owner-builders use a taper tap as the first step when cutting threads in a new hole. Starting with the wrong tap (such as a bottoming tap) makes it hard to get the threads straight and increases the chance of breaking the tool inside the hole.
Intuition Check
Do not read “tap” here as a light hit or a water faucet. In this term, a tap is a tool for cutting screw grooves inside a hole. Also, “taper tap” does not necessarily mean it cuts a tapered hole; the taper is on the starting end of the tool.
Example Sentence 1
The mechanic used a taper tap to begin cutting threads in the new mounting hole before switching to a plug tap to finish the job.
Example Sentence 2
Using the taper tap on the aluminum bracket prevented the tool from binding at the start of the cut.