6.3 Use of Common Tools
Key Takeaways
- The NCATT AET standard groups hand tools into striking (hammers/mallets), turning (screwdrivers, wrenches, taps/dies), gripping (pliers), and cutting (snips, hacksaws, chisels, files) categories, each with a specific correct use.
- Wrenches used for critical fasteners include spanner, torque, and Allen (hex) types — torque wrenches are required whenever a fastener has a specified torque value.
- Precision measuring tools — calipers, micrometers, and vernier scales — read to thousandths of an inch or finer, far tighter than a rule or combination set can achieve.
- Avionics connector work specifically requires wire strippers, crimpers, and pin extractors used together, matched to wire gauge and pin/contact size.
- Using a tool for a purpose it wasn't designed for (e.g., a screwdriver as a chisel, or a hammer struck at the wrong angle) is a leading cause of both aircraft damage and technician injury.
Overview: Tool Proficiency in Aviation Maintenance
Use of common tools is Official Standard #26 on the NCATT AET exam. The standard isn't about memorizing a catalog — it's about demonstrating that a technician can look at a task and select the tool best suited to it, understanding that some tools serve multiple purposes while others are highly specialized.
Striking, Turning, and Gripping Tools
| Tool | Primary Use | Notes |
|---|---|---|
| Hammers / mallets | Driving punches, seating parts, forming sheet metal | Soft-faced mallets protect finished surfaces; steel hammers are for punches and chisels only |
| Screwdrivers | Turning slotted, Phillips, or Torx fasteners | Blade width/type must match the screw head or it will damage the head |
| Pliers / cutting pliers | Gripping, bending, or cutting wire and small parts | Includes needle-nose, diagonal, and slip-joint variants |
| Punches | Marking a drill start point, driving out pins, aligning holes | Center punches start holes; pin punches drive out roll pins |
| Wrenches (spanner, torque, Allen) | Turning nuts, bolts, and hex-drive fasteners | A torque wrench is mandatory whenever a fastener has a specified torque value — hand-tight is not sufficient for structural or safety-critical hardware |
| Hand snips | Cutting sheet metal or lightweight stock | Straight and curved-blade variants for different cut radii |
| Hacksaws | Cutting metal stock, bolts, or tubing | Blade tooth count is chosen for material thickness |
| Chisels | Removing rivet heads, shearing material, rough shaping | Always struck with a hammer, never a wrench or pliers handle |
| Files | Smoothing edges, deburring, fitting parts | Cut only on the forward (push) stroke for most files |
Drilling, Measuring, and Layout Tools
Drilling Tools
Drills, twist drills, reamers, and countersinks each perform a distinct step in preparing a fastener hole:
- A twist drill cuts the initial round hole to a nominal diameter.
- A reamer follows the drill to bring the hole to a precise final diameter with a smooth wall — important for interference-fit fasteners.
- A countersink cuts the conical relief at the surface so a flush-head rivet or screw sits level with the skin.
Measuring and Layout Tools
| Tool | Precision Level | Typical Aviation Use |
|---|---|---|
| Rules / combination sets / scribers | Fractions of an inch | Marking cut lines, general layout |
| Engineering scales | Fine graduations, scaled drawings | Reading and laying out to drawing scale |
| Calipers | Thousandths of an inch | Measuring outside/inside diameters, depths |
| Micrometers | Ten-thousandths of an inch | Precise diameter/thickness checks (wire gauge, bearing fits) |
| Vernier scales | Thousandths of an inch | Fine adjustment reading on calipers and other precision tools |
| Magnifying glasses | N/A (visual aid) | Inspecting connector pins, cracks, and small stamped markings |
The further down this table you go, the tighter the tolerance the tool can resolve — a rule is fine for marking a cut line, but a micrometer is what you reach for when a dimension has to be verified against a tight aircraft specification.
Avionics-Specific and Threading Tools
Several tools on the standard's list are used almost exclusively in electrical and avionics work:
- Wire strippers remove insulation from a specific gauge of wire without nicking the conductor strands underneath — the wrong stripper setting either leaves insulation behind or weakens the wire.
- Crimpers mechanically attach a terminal or pin contact to a stripped wire end, forming a gas-tight connection; crimpers are sized and selected to match the contact's specified crimp cycle.
- Pin extractors remove a crimped contact from a connector housing without damaging the housing's retention clip, so the contact (or the connector) can be reused or replaced.
- Wire-marking devices print or sleeve an identifying label directly onto a wire, which is essential for traceability during troubleshooting.
- Multimeters (covered in depth elsewhere in this guide) round out the electrical toolkit for voltage, current, and resistance checks.
Taps and dies are the outlier on the list that apply to mechanical rather than electrical work — a tap cuts internal threads into a hole, and a die cuts external threads onto a rod or bolt blank, used when repairing damaged threads or fabricating a replacement fastener.
Proficiency and Safety
The exam standard emphasizes two judgment skills beyond simply naming tools:
- Choosing the tool best suited to the task. Some tools genuinely serve multiple purposes (a multimeter measures three different quantities; a combination set doubles as a rule, square, and depth gauge), but that flexibility doesn't mean any tool will do for any job — a screwdriver is not a substitute chisel, and a pair of pliers is not a substitute wrench.
- Using tools safely and caring for them. Improper hammer use — striking at the wrong angle, using a steel hammer where a soft-faced mallet belongs, or using a worn/mushroomed punch — is a leading cause of both aircraft skin and structure damage and technician injury (flying metal fragments, crushed fingers, eye injuries). Tools should be inspected before use, kept clean and properly stored, and replaced when worn, chipped, or out of calibration.
Worked Example: Replacing a Damaged Connector Pin
A technician finds a bent, non-repairable pin inside a multi-pin avionics connector during a continuity check. The repair sequence draws on exactly the tool categories above:
- Use a pin extractor sized to the connector's contact series to release the damaged pin's retention clip and withdraw it from the housing without damaging the housing itself.
- Cut the wire back past any stress point, then use a wire stripper set to the correct gauge to remove insulation cleanly from the new wire end, exposing strands without nicking them.
- Select a crimper matched to the new pin contact's specified crimp profile and complete the crimp — a mismatched or uncalibrated crimper produces a weak mechanical and electrical connection that can fail later under vibration.
- Use a magnifying glass to visually inspect the crimp for proper strand capture and no insulation intrusion into the contact barrel.
- Reinsert the new pin into the connector housing until the retention clip audibly or visibly seats, then verify with a multimeter that continuity through the repaired pin matches the adjacent, undamaged pins.
A fastener's installation instructions specify an exact torque value. Which tool must be used to install it correctly?
During a connector repair, which tool is used specifically to remove a crimped contact pin from its housing without damaging the housing's retention clip?
What is the most accurate description of improper hammer use in aircraft maintenance?