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PTT Public Company Limited, a Thai oil and gas company.

Part task trainer (military).

Partial thromboplastin time.

Partido Trabalhista Timorense.

Partitioning tracer test.

Pennsylvania Tunnel and Terminal Railroad, the owner of the tunnels to New York Penn Station.

The Petronas Twin Towers in Kuala Lumpur, Malaysia. Currently, the tallest twin buildings in the world.

Platform Terminal Transmitter, satellite tag for wildlife tracking.

Polytrimethylene terephtalate.

'''Post, Telegraph and Telephone''' from Iran.

Post Telefon Telegraph from Germany.

Post Tetanic Potentiation, a neurological phenomenon.

Postal Telegraph and Telephone (several).

Postal Telephone and Telegraph (several).

Poste, Téléphone et Télécommunications from France.

Prince's Trust Team program, set up in the UK by the Prince of Wales.

'''Professional Technology Temple''', the largest BBS in Taiwan.

Protein truncation test.

Public Telegraph and Telephone (several).

Public Telephone and Telegraph (several).

Push to talk.