Put Through (PT) Trading allows brokers to advertise their buy...

Put Through (PT) Trading allows brokers to advertise their buy or sell interests by announcing bid or offer prices. Members may then deal directly with each other, either on behalf of their clients or for themselves. Prices may be adjusted during the negotiation; hence, the effective executed price may not be the same as that advertised and may not follow the price spread rules. After concluding negotiations, dealers must send details of the result(s) for recording purposes.

In 2008, this was broken down further so P1 became a 'put through' trade with a value of > $1 million.