TPI
TPI turns up in 2 fields: fasteners, automotive. Here is what it means to the people in each one.
TPI in fasteners
Threads per inch: the count of thread crests in one inch of length, used to state the pitch of inch threads.
TPI stands for threads per inch, the number that follows the diameter in an inch thread callout, as in 3/8-16. Pitch is its reciprocal, so 16 TPI is a pitch of 0.0625 in. A screw pitch gauge or a steel rule laid along the crests reads it quickly, and on metric hardware the idea is replaced by pitch stated directly in millimeters.
"It's three-eighths, but I can't tell if it's 16 or 24 TPI, put the pitch gauge on it before you force a nut."
TPI in automotive
Tuned Port Injection is an early electronic fuel injection system used by General Motors.
Tuned Port Injection is a specific multi-port electronic fuel injection system introduced by General Motors for their older V8 engines. It uses long, tuned intake runners designed to boost low-end torque. While it drastically improved drivability over carburetors, the long runners restrict high-RPM airflow, limiting top-end horsepower.
"We're pulling the old TPI setup off the Camaro and swapping to a newer manifold for better top-end flow."