What is the difference between a thread chaser and a tap?
Short answer: A chaser cleans and reforms existing threads without removing much metal, while a tap cuts new threads; use chasers to clean damaged threads and taps to cut threads in new holes.
Damaged or dirty threads cause fasteners to bind and torque readings to be wrong. Thread chasers reshape threads, while taps cut metal and can weaken threads if used to clean.
Taps and dies are sold in sets in metric and SAE sizes. Outside thread chasers clean external threads on studs and bolts. Before chasing, identify the thread size and pitch with a thread gauge so you do not cross-cut the threads.
Use cutting oil, clear chips frequently, and turn slowly. Wear safety glasses and handle taps carefully, as they are brittle and can break.
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General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.